Projection type image display apparatus

ABSTRACT

A laser beam (L 50 ) generated by a laser light source ( 50 ) is reflected by a light beam scanning device ( 60 ) and irradiated onto a hologram recording medium ( 45 ). On the hologram recording medium ( 45 ), an image ( 35 ) of a scatter plate is recorded as a hologram by using reference light that converges on a scanning origin (B). The light beam scanning device ( 60 ) bends the laser beam (L 50 ) at the scanning origin ( 3 ) and irradiates the laser beam onto the hologram recording medium ( 45 ). At this time, scanning is carried out by changing a bending mode of the laser beam with time so that an irradiation position of the bent laser beam (L 60 ) on the hologram recording medium ( 45 ) changes with time. Regardless of an irradiation position of the beam, diffracted light (L 45 ) from the hologram recording medium ( 45 ) produces a reproduction image ( 35 ) of the scatter is plate on the spatial light modulator ( 200 ). The modulated image of the spatial light modulator ( 200 ) is projected onto a screen ( 400 ) by a projection optical system ( 300 ).

TECHNICAL FIELD

The present invention relates to a projection type image displayapparatus, and in particular, relates to a technology for displaying animage on a screen by illuminating a spatial light modulator using lightfrom a coherent light source.

BACKGROUND ART

As a projection type image display apparatus for displaying an image byprojecting light onto a screen, various types of apparatuses have beenproposed, including an apparatus commercially available, which is aso-called “optical projector.” A basic principle of such a projectiontype image display apparatus is to produce a two-dimensional originalimage by utilizing a spatial light modulator such as a liquid crystalmicrodisplay or a DMD (Digital Micromirror Device), and magnifies andprojects the two-dimensional original image on a screen by utilizing aprojection optical system.

A general optical projector adopts a system which illuminates a spatiallight modulator such as a liquid crystal display using a white lightsource such as a high pressure mercury lamp, magnifies a modulated imagethus obtained, by means of lenses and projects the same on a screen. Forexample, Japanese Unexamined Patent Publication No. 2004-264512discloses a technology that divides white light generated by anultrahigh pressure mercury lamp into three primary color components ofR, G, and B by means of a dichroic mirror, guides these lights tospatial light modulators for each primary color, synthesizes modulatedimages thus produced for the primary colors by means of a cross dichroicprism and projects a synthesized image on a screen.

However, the service life of a high brightness discharge lamp such as ahigh pressure mercury lamp is comparatively short, wherein if such alamp is utilized in an optical projector, etc., the lamp needs to befrequently replaced. Further, since it is necessary to utilize acomparatively large optical system such as a dichroic mirror to extractlights of the primary color components, there is a disadvantage that theentire apparatus becomes large-sized. Therefore, a system using acoherent light source such as a laser has been proposed. For example, asemiconductor laser, which is widely utilized in industry, has aremarkably long service life in comparison with a high brightnessdischarge lamp such as a high pressure mercury lamp. A1so, since thesemiconductor laser is a light source capable of producing light of asingle wavelength, a spectroscopic instrument such as a dichroic mirroris no longer required, and there is an advantage that the entireapparatus can be made small-sized.

On the other hand, in a system using a coherent light source such as alaser, a new problem of generating speckles is brought about. Thespeckles form a spot-like pattern appearing when coherent light such asa laser light is irradiated on a diffusing surface, and are observed asspot-like unevenness in brightness when they appear on a screen, andbecome a factor that physiologically causes harmful effects to anobserver.

For example, when one point on a screen is indicated with a laserpointer, the spot of the laser light appears as a bright glare on thescreen. This is caused by the occurrence of speckle noise on the screen.It is considered that the reason why speckles are caused when coherentlight is used is that coherent lights reflected at portions of thediffusing and reflecting surface of a screen, etc., interfere with eachother due to extremely high coherency. For example, a detailedtheoretical consideration on occurrence of speckles is described in“Speckle Phenomena in Optics, Joseph W. Goodman, Roberts & Co., 2006.”

In use as a laser pointer or the like, a small spot is only seen by anobserver, so that a severe problem does not occur. However, when a laserlight source is used as an image display apparatus, an image must bedisplayed on the entire screen having a wide region, so that if specklesoccur on the screen, they give physiologically harmful effect to anobserver to cause symptoms such as feeling sick.

Of course, several detailed methods for reducing the above-describedspeckle noise have been proposed. For example, Japanese UnexaminedPatent Publication No. H06-208089 discloses a technology by which laserlight is irradiated onto a scatter plate, scattered light obtained fromthe scatter plate is guided to a spatial light modulator and the scatterplate is driven to rotate by a motor, whereby reducing speckles. A1so,Japanese Unexamined Patent Publication No. 2004-144936 discloses atechnology for reducing speckles by oscillating a scatter plate disposedbetween a laser light source and a spatial light modulator.

However, to rotate or oscillate the scatter plate, a large-scalemechanical drive mechanism is required, so that the apparatus isentirely increased in size, and power consumption is also increased.With this method, light from the laser light source is scattered by thescatter plate, so that a part of the laser light does not contribute toimage display at all and is wasted. Further, even when the scatter plateis rotated or oscillated, the position of the optical axis of theillumination light does not change, so that speckles occurring on thediffusing surface of the screen cannot be sufficiently reduced.

Therefore, an object of the present invention is to provide a technologyfor efficiently and sufficiently reducing the occurrence of speckles ina projection type image display apparatus using a coherent light source.

DISCLOSURE OF INVENTION

(1) The first feature of the present invention resides in a projectiontype image display apparatus that carries out image display byprojecting light onto a screen, comprising:

a spatial light modulator that modulates incident light according to anincidence position based on an image as a display object, and emits thelight;

an illumination unit that supplies illumination light to the spatiallight modulator; and

a projection optical system that guides illumination light modulated bythe spatial light modulator to the screen, and projects the image ontothe screen, wherein

the illumination unit includes:

a coherent light source that generates a coherent light beam,

a hologram recording medium on which an image of a scatter plate isrecorded, and

a light beam scanning device that irradiates the light beam onto thehologram recording medium, and scans the light beam so that theirradiation position of the light beam on the hologram recording mediumchanges with time,

the image of the scatter plate is recorded as a hologram on the hologramrecording medium by using reference light irradiated along an opticalpath,

the coherent light source generates a light beam with a wavelengthcapable of reproducing the image of the scatter plate,

the light beam scanning device scans the light beam so that theirradiation direction of the light beam with respect to the hologramrecording medium is along the optical path of the reference light, and

the spatial light modulator is disposed at a production position of thereproduction image of the scatter plate obtained from the hologramrecording medium.

(2) The second feature of the present invention resides in theprojection type image display apparatus having the first feature,wherein

the light beam scanning device bends the light beam at a scanningorigin, irradiates the bent light beam onto the hologram recordingmedium, and changes an irradiation position of the bent light beam onthe hologram recording medium with time by changing a bending mode ofthe light beam with time,

the image of the scatter plate is recorded as a hologram on the hologramrecording medium by using reference light that converges on a specificconvergence point or reference light that diverges from a specificconvergence point, and

the light beam scanning device scans the light beam by setting theconvergence point as the scanning origin.

(3) The third feature of the present invention resides in the projectiontype image display apparatus having the second feature, wherein

the image of the scatter plate is recorded on the hologram recordingmedium by using reference light that three-dimensionally converges ordiverges along a side surface of a cone whose tip is on the convergencepoint.

(4) The fourth feature of the present invention resides in theprojection type image display apparatus having the third feature,wherein

the light beam scanning device has a function of bending the light beamso that the light beam swings on a plane including the scanning origin,and scans the light beam in a one-dimensional direction on the hologramrecording medium.

(5) The fifth feature of the present invention resides in the projectiontype image display apparatus having the third feature, wherein

the light beam scanning device has a function of bending the light beamso that the light beam swings on a first plane including the scanningorigin and a function of bending the light beam so that the light beamswings on a second plane including the scanning origin and orthogonal tothe first plane, and scans the light beam in two-dimensional directionson the hologram recording medium.

(6) The sixth feature of the present invention resides in the projectiontype image display apparatus having the second feature, wherein

the image of the scatter plate is recorded on the hologram recordingmedium by using reference light that two-dimensionally converges ordiverges along a plane including the convergence point.

(7) The seventh feature of the present invention resides in theprojection type image display apparatus having the sixth feature,wherein

the light beam scanning device has a function of bending the light beamso that the light beam swings on a plane including the scanning origin,and scans the light beam in a one-dimensional direction on the hologramrecording medium.

(8) The eighth feature of the present invention resides in theprojection type image display apparatus having the first feature,wherein

the light beam scanning device changes the irradiation position of thelight beam on the hologram recording medium with time by irradiating thelight beam onto the hologram recording medium while moving the lightbeam parallel,

the image of the scatter plate is recorded as a hologram on the hologramrecording medium by using reference light composed of a parallel lightflux, and

the light beam scanning device scans the light beam by irradiating thelight beam onto the hologram recording medium in a direction parallel tothe reference light.

(9) The ninth feature of the present invention resides in the projectiontype image display apparatus having any one of the first to eighthfeatures, wherein

the coherent light source is a laser light source that generates a laserbeam.

(10) The tenth feature of the present invention resides in theprojection type image display apparatus having any one of the first toninth features, wherein

the hologram recording medium records the image of the scatter plate asa volume hologram.

(11) The eleventh feature of the present invention resides in theprojection type image display apparatus having any one of the first toninth features, wherein

the hologram recording medium records the image of the scatter plate asa surface relief hologram.

(12) The twelfth feature of the present invention resides in theprojection type image display apparatus having any one of the first toninth features, wherein

the hologram recorded on the hologram recording medium is a computergenerated hologram.

(13) The thirteenth feature of the present invention resides in theprojection type image display apparatus having any one of the first toninth features, wherein

the hologram recorded on the hologram recording medium is a Fouriertransform hologram.

(14) The fourteenth feature of the present invention resides in theprojection type image display apparatus having any one of the first toninth features, wherein

the hologram recorded on the hologram recording medium is a reflectiontype hologram, and reflected diffracted light of the light beam is usedas illumination light.

(15) The fifteenth feature of the present invention resides in theprojection type image display apparatus having any one of the first toninth features, wherein

the hologram recorded on the hologram recording medium is a transmissiontype hologram, and transmitted diffracted light of the light beam isused as illumination light.

(16) The sixteenth feature of the present invention resides in theprojection type image display apparatus having any one of the first tofifteenth features, wherein

the light beam scanning device is a scanning mirror device, a totalreflection prism, a refracting prism, or an electro-optic crystal.

(17) The seventeenth feature of the present invention resides in theprojection type image display apparatus having any one of the first tosixteenth features, wherein

the spatial light modulator comprises a transmission type or reflectiontype liquid crystal display, a transmission type or reflection type LCOSdevice, or a digital micromirror device.

(18) The eighteenth feature of the present invention resides in theprojection type image display apparatus having any one of the first toseventeenth features, wherein

the projection optical system carries out front projection forprojecting an image onto an observing surface side of the screen.

(19) The nineteenth feature of the present invention resides in theprojection type image display apparatus having any one of the first toeighteenth features, wherein

the coherent light source includes three laser light sources thatgenerate monochromatic laser beams with wavelengths of three primarycolors, respectively, and a light synthesizer that produces asynthesized light beam by synthesizing laser beams generated by thethree laser light sources,

the light beam scanning device scans the synthesized light beam producedby the light synthesizer on the hologram recording medium,

the image of the scatter plate is recorded as three holograms on thehologram recording medium so that reproduction images are obtained bythe laser beams generated by the three laser light sources, and

the spatial light modulator has a pixel array spatially disposed, whereany of the three primary colors is assigned to each pixel, and has afunction of modulating light on a pixel basis independently, and filtersof the corresponding primary colors are provided at respective positionsof the pixels.

(20) The twentieth feature of the present invention resides in theprojection type image display apparatus having any one of the first toeighteenth features, comprising:

a first spatial light modulator that carries out modulation based on afirst image having a first primary color component;

a first illumination unit that supplies first illumination light with awavelength corresponding to the first primary color to the firstspatial, light modulator;

a second spatial light modulator that carries out modulation based on asecond image having a second primary color component;

a second illumination unit that supplies second illumination light witha wavelength corresponding to the second primary color to the secondspatial light modulator;

a third spatial light modulator that carries out modulation based on athird image having a third primary color component; and

a third illumination unit that supplies third illumination light with awavelength corresponding to the third primary color to the third spatiallight modulator, wherein

the projection optical system guides illumination light modulated by thefirst spatial light modulator, illumination light modulated by thesecond spatial light modulator, and illumination light modulated by thethird spatial light modulator to the screen, and superimposes andprojects the first image, the second image, and the third image on thescreen.

(21) The twenty-first feature of the present invention resides in theprojection type image display apparatus having any one of the first toeighteenth features, comprising:

a first spatial light modulator that carries out modulation based on afirst image having a first primary color component;

a second spatial light modulator that carries out modulation based on asecond image having a second primary color component; and

a third spatial light modulator that carries out modulation based on athird image having a third primary color component, wherein

the coherent light source includes a first laser light source thatgenerates a first laser beam with a wavelength corresponding to thefirst primary color, a second laser light source that generates a secondlaser beam with a wavelength corresponding to the second primary color,a third laser light source that generates a third laser beam with awavelength corresponding to the third primary color, and a lightsynthesizer that produces a synthesized light beam by synthesizing laserbeams generated by the three laser light sources,

the light beam scanning device scans the synthesized light beam producedby the light synthesizer on the hologram recording medium,

the image of the scatter plate is recorded as three holograms on thehologram recording medium so that reproduction images are obtained bythe laser beams generated by the three laser light sources,

the illumination unit further includes a switching device that carriesout time-divisional supplying operations to supply illumination lightobtained from the hologram recording medium to the first spatial lightmodulator in a first period, supply the illumination light to the secondspatial light modulator in a second period, and supply the illuminationlight to the third spatial light modulator in a third period, and

the first laser light source generates the first laser beam in the firstperiod, the second laser light source generates the second laser beam inthe second period, and the third laser light source generates the thirdlaser beam in the third period.

(22) The twenty-second feature of the present invention resides in theprojection type image display apparatus having any one of the first toeighteenth features, wherein

the spatial light modulator carries out time-divisional modulatingoperations to carry out modulation based on a first image having a firstprimary color component in a first period, carry out modulation based ona second image having a second primary color component in a secondperiod, and carry out modulation based on a third image having a thirdprimary color component in a third period,

the coherent light source includes a first laser light source thatgenerates a first laser beam with a wavelength corresponding to thefirst primary color, a second laser light source that generates a secondlaser beam with a wavelength corresponding to the second primary color,a third laser light source that generates a third laser beam with awavelength corresponding to the third primary color, and a lightsynthesizer that produces a synthesized light beam by synthesizing laserbeams generated by the three laser light sources,

the light beam scanning device scans the synthesized light beam producedby the light synthesizer on the hologram recording medium,

the image of the scatter plate is recorded as three holograms on thehologram recording medium so that reproduction images are obtained bylaser beams generated by the three laser light sources, and

the first laser light source generates the first laser beam in the firstperiod, the second laser light source generates the second laser beam inthe second period, and the third laser light source generates the thirdlaser beam in the third period.

(23) The twenty-third feature of the present invention resides in aspatial light modulator illumination method in a projection type imagedisplay apparatus, for illuminating a spatial light modulator in aprojection type image display apparatus that carries out image displayby supplying illumination light to the spatial light modulator andprojecting modulated illumination light onto a screen, comprising:

a preparation step of creating a hologram recording medium by recordingan image of a scatter plate as a hologram on a recording medium; and

an illumination step of irradiating a coherent light beam onto thehologram recording medium in a state where the spatial light modulatoris disposed at a production position of a reproduction image of thescatter plate, and scanning the light beam on the hologram recordingmedium so that an irradiation position changes with time, wherein

in the preparation step, the hologram recording medium is created byirradiating coherent illumination light onto the scatter plate, usingscattered light obtained from the scatter plate as object light andirradiating the object light onto the recording medium along an opticalpath, using coherent light with the same wavelength as that of theillumination light as reference light, and recording interferencefringes formed by the object light and the reference light on therecording medium, and

in the illumination step, a light beam with a wavelength capable ofreproducing the image of the scatter plate is scanned so as to advancetoward an irradiation position on the hologram recording medium bypassing through an optical path along the optical path of the referencelight.

(24) The twenty-fourth feature of the present invention resides in thespatial light modulator illumination method in a projection type imagedisplay apparatus having the twenty-third feature, wherein

in the preparation step, by condensing a light flux of substantiallyparallel coherent light by using a convex lens having a focal point on aposition of convergence point, reference light that three-dimensionallyconverges on the convergence point or reference light thatthree-dimensionally diverges from the convergence point is produced, andby using the produced reference light, interference fringes arerecorded.

(25) The twenty-fifth feature of the present invention resides in thespatial light modulator illumination method in a projection type imagedisplay apparatus having the twenty-third feature, wherein

in the preparation step, by condensing a light flux of substantiallyparallel coherent light on a condensing axis by using a cylindrical lenshaving a central axis parallel to the condensing axis, reference lightthat two-dimensionally converges on a point on the condensing axis orreference light that two-dimensionally diverges from a point on thecondensing axis is produced, and by using the produced reference light,interference fringes are recorded.

(26) The twenty-sixth feature of the present invention resides in thespatial light modulator illumination method in a projection type imagedisplay apparatus having the twenty-third feature, wherein

in the preparation step, interference fringes are recorded by usingreference light composed of a parallel light flux.

(27) The twenty-seventh feature of the present invention resides in thespatial light modulator illumination method in a projection type imagedisplay apparatus having any one of the twenty-third to twenty-sixthfeatures, wherein

a computer generated hologram is recorded on the hologram recordingmedium by carrying out the process of the preparation step by asimulation operation using a virtual scatter plate.

(28) The twenty-eighth feature of the present invention resides in thespatial light modulator illumination method in a projection type imagedisplay apparatus having the twenty-seventh feature, wherein

a model including a large number of point light sources aligned in agrid pattern on a plane is used as the virtual scatter plate.

(29) The twenty-ninth feature of the present invention resides in aprojection type image display apparatus that carries out image displayby projecting light onto a screen, comprising:

a spatial light modulator that modulates incident light according to anincidence position based on an image as a display object, and emits themodulated light:

an illumination unit that supplies illumination light to the spatiallight modulator; and

a projection optical system that guides illumination light modulated bythe spatial light modulator to the screen and projects the image ontothe screen, wherein

the illumination unit includes

a coherent light source that generates a coherent light beam,

a microlens array including a collection of a large number ofindependent lenses; and

a light beam scanning device that irradiates the light beam onto themicrolens array and carries out scanning so that an irradiation positionof the light beam on the microlens array changes with time, wherein

each of the independent lenses included in the microlens array has afunction of refracting light irradiated from the light beam scanningdevice and forming an irradiation region on a light receiving surface ofthe spatial light modulator, and is configured so that irradiationregions formed by the independent lenses become substantially a samecommon region on the light receiving surface.

(30) The thirtieth feature of the present invention resides in theprojection type image display apparatus having the twenty-ninth feature,wherein

the light beam scanning device bends the light beam at a scanning originand irradiates the light beam onto the microlens array, and changes abending mode of the light beam with time so that an irradiation positionof the bent light beam on the microlens array changes with time, and

each of the independent lenses included in the microlens array refractslight incident from the scanning origin to form a common irradiationregion on the light receiving surface of the spatial light modulator.

(31) Thee thirty-first feature of the present invention resides in aprojection type image display apparatus that carries out image displayby projecting light onto a screen, comprising:

a spatial light modulator that modulates incident light according to anincidence position based on an image as a display object, and emits themodulated light;

an illumination unit that supplies illumination light to the spatiallight modulator; and

a projection optical system that guides illumination light modulated bythe spatial light modulator to the screen and projects the image ontothe screen, wherein

the illumination unit includes

a coherent light source that generates a coherent light beam,

a light beam scanning device that carries out beam scanning bycontrolling either or both of a direction and a position of the lightbeam, and

an optical diffusing element that diffuses an incident light beam andemits a light beam, wherein

the light beam scanning device guides a light beam generated by thecoherent light source toward the optical diffusing element, and carriesout scanning so that an incidence position of the guided light beam onthe optical diffusing element changes with time, and

the optical diffusing element has a function of forming irradiationregions on a light receiving surface of the spatial light modulator bydiffusing an incident light beam, and is configured so that the formedirradiation regions become substantially a same common region on thelight receiving surface regardless of an incidence position of theincident light beam.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is an optical system arrangement drawing showing a process ofcreating a hologram recording medium as a component of a projection typeimage display apparatus according to the present invention.

FIG. 2 is a plan view showing a position relationship between a sectionS1 of reference light L23 and a hologram photosensitive medium 40 in theprocess shown in FIG. 1.

FIG. 3 is a plan view showing a position relationship between anothersection S2 of the reference light L23 and the hologram photosensitivemedium 40 in the process shown in FIG. 1.

FIG. 4 is a partial enlargement view around a scatter plate 30 and thehologram photosensitive medium 40 in the optical system shown in FIG. 1.

FIG. 5 is a view showing a process of reproducing an image 35 of thescatter plate by using the hologram recording medium 45 created by theprocess shown in FIG. 1.

FIG. 6 is a view showing a process of reproducing an image 35 of thescatter plate by irradiating only one light beam onto the hologramrecording medium 45 created by the process shown in FIG. 1.

FIG. 7 is another view showing the process of reproducing the image 35of the scatter plate by irradiating only one light beam onto thehologram recording medium 45 created by the process shown in FIG. 1.

FIG. 8 is a plan view showing irradiation positions of light beams inthe reproduction process shown in FIG. 6 and FIG. 7.

FIG. 9 is a side view showing a configuration of an illumination unit100 used in a projection type image display apparatus according to abasic embodiment of the present invention.

FIG. 10 is a side view showing a state where an illuminating object 70is illuminated by using the illumination unit 100 shown in FIG. 9.

FIG. 11 is a plan view showing a configuration of a projection typeimage display apparatus using the illumination unit 100 shown in FIG. 9.

FIG. 12 is a plan view showing a first example of a scanning mode of alight beam on the hologram recording medium 45 in the illumination unit100 shown in FIG. 9.

FIG. 13 is a plan view showing a second example of a scanning mode of alight beam on the hologram recording medium 45 in the illumination unit100 shown in FIG. 9.

FIG. 14 is a plan view showing a third example of a scanning mode of alight beam on the hologram recording medium 45 in the illumination unit100 shown in FIG. 9.

FIG. 15 is a plan view showing a fourth example of a scanning mode of alight beam on the hologram recording medium 45 in the illumination unit100 shown in FIG. 9.

FIG. 16 is a plan view showing a scanning mode of a light beam when aband-shaped hologram recording medium 85 is used.

FIG. 17 is an optical system arrangement drawing showing a process ofcreating the band-shaped hologram recording medium 85 shown in FIG. 16.

FIG. 18 is a side view showing the principle of creating a hologramrecording medium as a component of a projection type image displayapparatus according to the present invention by means of CGH.

FIG. 19 is a front view of a virtual scatter plate 30′ shown in FIG. 18.

FIG. 20 is a table showing experimental results in which a specklereducing effect is obtained according to the present invention.

FIG. 21 is a view showing a configuration example of a light source whena color image is to be displayed with a projection type image displayapparatus according to the present invention.

FIG. 22 is a plan view showing a spatial light modulator 200 and a colorfilter 250 used when a color image is displayed with the light sourceshown in FIG. 21.

FIG. 23 is a drawing showing another configuration example fordisplaying a color image with a projection type image display apparatusaccording to the present invention.

FIG. 24 is a side view showing a process of creating a reflection typehologram recording medium by using convergent reference light.

FIG. 25 is a side view showing a reproduction process of the reflectiontype hologram recording medium 45 created by the method shown in FIG.24.

FIG. 26 is a side view showing a process of creating a transmission typehologram recording medium by using convergent reference light.

FIG. 27 is a side view showing a reproduction process of thetransmission type hologram recording medium 45 created by the methodshown in FIG. 26.

FIG. 28 is a side view showing a preparation process when a hologramrecording medium is created by using divergent reference light.

FIG. 29 is a side view showing a reproduction process of the preparatoryhologram recording medium 95 created in the preparation process shown inFIG. 28.

FIG. 30 is a side view showing a process of creating a reflection typehologram recording medium by using divergent reference light.

FIG. 31 is a side view showing a process of creating a transmission typehologram recording medium by using divergent reference light.

FIG. 32 is a side view showing another preparation process when ahologram recording medium is created by using divergent reference light.

FIG. 33 is a side view showing a reproduction process of the preparatoryhologram recording medium 95 created in the preparation process shown inFIG. 32.

FIG. 34 is an optical system arrangement drawing showing a process ofcreating a hologram recording medium as a component of a projection typeimage display apparatus according to a modification of the presentinvention.

FIG. 35 is a side view showing a basic configuration of an illuminationunit 110 used for a projection type image display apparatus according tothe modification of the present invention.

FIG. 36 is a side view showing a basic configuration of an illuminationunit 120 used for a projection type image display apparatus according toanother modification of the present invention.

FIG. 37 is a side view showing an operation principle of theillumination unit 120 shown in FIG. 36.

BEST MODE FOR CARRYING OUT THE INVENTION <<<Section 1. HologramRecording Medium Used in the Present Invention>>>

First, a description is given of features of a hologram recording mediumto be used as a component of a projection type image display apparatusaccording to an embodiment of the present invention. FIG. 1 is anoptical system arrangement drawing showing a process of creating thishologram recording medium. With this optical system, a hologramrecording medium on which an image of a scatter plate is recorded iscreated.

A coherent light source 10 shown at the upper right of the drawingproduces a coherent light beam L10, and in actuality, a laser lightsource that generates a monochromatic laser light having a circularsection is used. The coherent light beam L10 produced by this laserlight source is split into two beams by a beam splitter 20.Specifically, a part of the light beam L10 is directly transmittedthrough the beam splitter 20 and guided to the lower side of thedrawing, and the other part of the light beam is reflected by the beamsplitter 20 and guided as a light beam L20 to the left side of thedrawing.

The light beam L10 transmitted through the beam splitter 20 performs therole of generating object light Lobj of the scatter plate. Specifically,the light beam L10 that advanced to the lower side of the drawing isreflected by a reflecting mirror 11 to become a light beam L11, andfurther, expanded in diameter by a beam expander 12 to compose aparallel light flux L12, and irradiated onto the entire region of theright side surface of the scatter plate 30. The scatter plate 30 is aplate having a property of scattering irradiated light, and is alsogenerally called an optical diffuser plate. In the embodiment shownherein, a transmission type scatter plate (for example, opal glassplate) into which microparticles (light scatterers) for scattering lightinside are kneaded is used. Therefore, as illustrated, the parallellight flux L12 irradiated onto the right side surface of the scatterplate 30 is transmitted through the scatter plate 30 and emits asscattered light L30 from the left side surface. This scattered light L30composes object light Lobj of the scatter plate 30.

On the other hand, the light beam L20 reflected by the beam splitter 20performs the role of generating reference light Lref. Specifically, thelight beam L20 that advanced to the left side of the drawing from thebeam splitter 20 is reflected by the reflecting mirror 21 to become alight beam L21, and further, expanded in diameter by the beam expander22 to compose a parallel light flux L22, refracted by a convex lens 23having a focal point on the point C, and then irradiated onto a hologramphotosensitive medium 40. Even when the parallel light flux L22 iscomposed of a collection of parallel light beams not necessarilystrictly parallel to each other, there is no problem in practical use,as far as the parallel light flux L22 is composed of a collection oflight beams substantially parallel to each other. The hologramphotosensitive medium 40 is a photosensitive medium to be used forrecording a hologram image. Irradiation light L23 to be irradiated ontothe hologram photosensitive medium 40 composes reference light Lref.

Finally, onto the hologram photosensitive medium 40, the object lightLobj of the scatter plate 30 and the reference light Lref areirradiated.

Here, the object light Lobj and the reference light Lref are coherentlights both having the same wavelength λ produced by the coherent lightsource 10 (laser light source), so that interference fringes of theselights are recorded on the hologram photosensitive medium 40. In otherwords, on the hologram photosensitive medium 40, an image of the scatterplate 30 is recorded as a hologram.

FIG. 2 is a plan view showing the position relationship between thesection S1 of the reference light L23 (Lref) and the hologramphotosensitive medium 40 shown in FIG. 1. The parallel light flux L22expanded in diameter by the beam expander 22 has a circular section, sothat the reference light Lref condensed by the convex lens 23 convergesin a conical shape whose tip is on the focal point C of the lens.However, in the example shown in FIG. 1, the hologram photosensitivemedium 40 is disposed obliquely to the central axis of this cone, sothat the section S1 cutting the reference light L23 (Lref) by thesurface of the hologram photosensitive medium 40 becomes oval as shownin FIG. 2.

Thus, in the example shown in FIG. 2, the reference light Lref isirradiated into only the region hatched in the drawing of the entireregion of the hologram photosensitive medium 40, so that the hologram ofthe scatter plate 30 is recorded in only this hatched region. Of course,it is also possible that the whole hologram photosensitive medium 40 isincluded in the section S2 of the reference light Lref as shown in theexample shown in FIG. 3 by producing a parallel light flux L22 with alarger diameter by the beam expander 22 and using a convex lens 23 witha larger diameter. In this case, as shown with hatching in the drawing,the hologram of the scatter plate 30 is recorded on the entire surfaceof the hologram photosensitive medium 40. When creating a hologramrecording medium to be used in the present invention, recording can becarried out in either of the modes shown in FIG. 2 and FIG. 3.

Next, a detailed description is given of the optical process ofrecording the image of the scatter plate 30 on the hologramphotosensitive medium 40. FIG. 4 is a partial enlargement view aroundthe scatter plate 30 and the hologram photosensitive medium 40 in theoptical system shown in FIG. 1. As described above, the reference lightLref is obtained by condensing the parallel light flux L22 having acircular section by the convex lens 23 having the focal point C, and thereference light Lref converges in a conical shape whose tip is on thefocal point C. Hereinafter, this focal point C is referred to as aconvergence point. As illustrated, the reference light L23 (Lref)irradiated onto the hologram photosensitive medium 40 converges on thisconvergence point C.

On the other hand, light (object light Lobj) emitted from the scatterplate 30 is scattered light, and advances in various directions. Forexample, as illustrated, assuming an object point Q1 on the upper end ofthe left side surface of the scatter plate 30, scattered light isemitted in all directions from this object point Q1. Similarly,scattered light is also emitted in all directions from arbitrary objectpoints Q2 and Q3. Therefore, focusing attention on an arbitrary point P1within the hologram photosensitive medium 40, information oninterference fringes formed by object lights L31, L32, and L33 from theobject points Q1, Q2, and Q3 and the reference light Lref advancingtoward the convergence point C is recorded. Of course, in actuality,object points on the scatter plate 30 are not only Q1, Q2, and Q3, sothat similarly, information from all object points on the scatter plate30 is recorded as information on interference fringes formed byinterference with the reference light Lref. In other words, on theillustrated point P1, all information of the scatter plate 30 isrecorded. In exactly the same manner, all information of the scatterplate 30 is also recorded on the illustrated point P2. Thus, allinformation of the scatter plate 30 is recorded on each portion of thehologram photosensitive medium 40. This is the essence of a hologram.

Hereinafter, the hologram photosensitive medium 40 on which informationof the scatter plate 30 is recorded by the above-described method isreferred to as a hologram recording medium 45. To obtain a hologramreproduction image of the scatter plate 30 by reproducing the hologramrecording medium 45, coherent light with the same wavelength as that ofthe light used for recording is irradiated as illumination light forreproduction from a direction corresponding to the reference light Lrefused for recording.

FIG. 5 is a view showing a process of reproducing an image 35 of thescatter plate by using the hologram recording medium 45 created by theprocess shown in FIG. 4. As illustrated, illumination light forreproduction Lrep is irradiated onto the hologram recording medium 45from the lower side. This illumination light for reproduction Lrep iscoherent light that diverges as a spherical wave from a point lightsource positioned at the convergence point C, and a part of theillumination light for reproduction becomes light to irradiate thehologram recording medium 45 while diffusing in a conical shape asillustrated. The wavelength of this illumination light for reproductionLrep is equal to the wavelength used for recording on the hologramrecording medium 45 (that is, the wavelength of coherent light generatedby the coherent light source 10 shown in FIG. 1),

Here, the position relationship between the hologram recording medium 45and the convergence point C shown in FIG. 5 is exactly the same as theposition relationship between the hologram photosensitive medium 40 andthe convergence point C shown in FIG. 4. Therefore, the illuminationlight for reproduction Lrep shown in FIG. 5 corresponds to light thatreverses on the optical path of the reference light Lref shown in FIG.4. When the illumination light for reproduction Lrep meeting theseconditions is irradiated onto the hologram recording medium 45, bydiffracted light L45 (Ldif) thereof, the hologram reproduction image 35(shown by the dashed line in the drawing) of the scatter plate 30 isobtained. The position relationship between the hologram recordingmedium 45 and the reproduction image 35 shown in FIG. 5 is exactly thesame as the position relationship between the hologram photosensitivemedium 40 and the scatter plate 30 shown in FIG. 4.

Thus, the technology for recording an image of an arbitrary object as ahologram and reproducing it is a known technology put into practical usefrom a long time ago. However, when creating a hologram recording mediumto be utilized for general use, a parallel light flux is used asreference light Lref. To reproduce the hologram recorded by usingreference light Lref consisting of a parallel light flux, illuminationlight for reproduction Lrep consisting of a parallel light flux is alsoutilized, and this is convenient.

On the other hand, when light that converges on the convergence point Cis utilized as reference light Lref as shown in FIG. 4, when carryingout reproduction, as shown in FIG. 5, light that diverges from theconvergence light C must be used as illumination light for reproductionLrep. In actuality, to obtain the illumination light for reproductionLrep shown in FIG. 5, an optical system such as a lens must be disposedat a specific position. If the position relationship between thehologram recording medium 45 and the convergence point C when carryingout reproduction does not match the position relationship between thehologram photosensitive medium 40 and the convergence point C whencarrying out recording, an accurate reproduction image 35 cannot beobtained, so that the illumination conditions when carrying outreproduction are limited (when reproduction is carried out by using aparallel light flux, only the irradiation angle must be satisfied amongthe illumination conditions).

For this reason, a hologram recording medium created by using referencelight Lref that converges on the convergence point C is not suitable forgeneral use. Even so, the reason why light that converges on theconvergence point C is used as reference light Lref in the embodimentdescribed herein is for making light beam scanning easy when carryingout reproduction. Specifically, in FIG. 5, for convenience ofdescription, a method for producing the reproduction image 35 of thescatter plate 30 by using illumination light for reproduction Lrepdiverging from the convergence point C is shown, however, in the presentinvention, in actuality, reproduction using the illumination light forreproduction Lrep diffusing in a conical shape as illustrated is notcarried out. Instead of this, a method in which a light beam is scannedis adopted. Hereinafter, a detailed description is given of this method.

FIG. 6 is a drawing showing a process of reproducing the image 35 of thescatter plate 30 by irradiating only one light beam onto the hologramrecording medium 45 created by the process shown in FIG. 4.Specifically, in this example, only one light beam L61 advancing towardone point P1 within the medium from the convergence point C is given asillumination light for reproduction Lrep. Of course, the light beam L61is coherent light with the same wavelength as that of light forrecording. As described above with reference to FIG. 4, on the arbitrarypoint P1 within the hologram recording medium 45, all information of thescatter plate 30 is recorded. Therefore, by irradiating illuminationlight for reproduction Lrep onto the position of the point P1 shown inFIG. 6 under conditions corresponding to the reference light Lref usedfor recording, the reproduction image 35 of the scatter plate 30 can beproduced by using only interference fringes recorded near this point P1.FIG. 6 shows a state where the reproduction image 35 is reproduced bythe diffracted light L45 (Ldif) from the point P1.

On the other hand, FIG. 7 shows an example in which only one light beamL62 advancing toward another point P2 within the medium from theconvergence point C is given as illumination light for reproductionLrep. In this case, all information of the scatter plate 30 is alsorecorded on the point P2, so that by irradiating the illumination lightfor reproduction Lrep onto the position of the point P2 under conditionscorresponding to the reference light Lref used for recording, thereproduction image 35 of the scatter plate 30 can be produced by usingonly interference fringes recorded near the point P2. FIG. 7 shows astate where the reproduction image 35 is reproduced by the diffractedlight L45 (Ldif) from the point P2. The reproduction image 35 shown inFIG. 6 and the reproduction image 35 shown in FIG. 7 are of the samescatter plate 30 as the original image, so that the reproduction imagesare theoretically identical to each other and produced at the sameposition.

FIG. 8 is a plan view showing an irradiation position of a light beam inthe reproduction process shown in FIG. 6 and FIG. 7. The point P1 shownin FIG. 8 corresponds to the point P1 shown in FIG. 6, and the point P2shown in FIG. 8 corresponds to the point P2 shown in FIG. 7. Thereference symbols A1 and A2 each denote sections of the illuminationlight for reproduction Lrep. The shapes and sizes of the sections A1 andA2 depend on the shapes and sizes of the sections of the light beams L61and L62. They also depend on the irradiation positions on the hologramrecording medium 45. Here, for convenience, circular sections A1 and A2are shown, however, in actuality, when light beams L61 and L62 havingcircular sections are used, the sectional shapes become oval shapesflattened according to the irradiation positions.

Thus, the contents of the interference fringes recorded near the pointP1 and near the point P2 shown in FIG. 8 are completely different fromeach other, however, whichever point a light beam that becomesillumination light for reproduction Lrep is irradiated onto, the samereproduction image 35 is obtained at the same position. This is becausethe illumination light for reproduction Lrep is a light beam advancingtoward each point P1 and P2 from the convergence point C, so that theillumination light for reproduction Lrep in the direction correspondingto the direction of the reference light Lref when carrying out recordingshown in FIG. 4 is given to each point.

The same applies, of course, to an arbitrary point on the hologramrecording medium 45 although FIG. 8 illustrates only two points P1 andP2. Therefore, when a light beam is irradiated onto an arbitrary pointon the hologram recording medium 45, as long as the light beam is lightfrom the convergence point C, the same reproduction image 35 is obtainedat the same position. In fact, as shown in FIG. 2, when a hologram isrecorded on only a region (hatched region in the drawing) that is a partof the hologram photosensitive medium 40, the reproduction image 35 isobtained only when a light beam is irradiated onto a point within theregion.

Finally, the hologram recording medium 45 described herein has featuresthat it is a medium on which an image of the scatter plate 30 isrecorded as a hologram by using the reference light Lref that convergeson the specific convergence point C, and when a light beam passingthrough this convergence point C is irradiated as illumination light forreproduction Lrep onto an arbitrary position, a reproduction image 35 ofthe scatter plate 30 is produced. Therefore, when a light beam passingthrough the convergence point C is scanned as illumination light forreproduction Lrep on the hologram recording medium 45, by diffractedlights Ldif obtained from respective irradiation points, the samereproduction image 35 is reproduced at the same position.

<<<Section 2. Projection Type Image Display Apparatus According to BasicEmbodiment of the Present Invention>>>

The feature of the present invention resides in a projection type imagedisplay apparatus wherein a peculiar illumination unit having a functionof reducing speckles is applied. Therefore, first, a description isgiven of a configuration of an illumination unit 100 used for aprojection type image display apparatus according to a basic embodimentof the present invention with reference to the side view of FIG. 9. Asillustrated, this illumination unit 100 includes a hologram recordingmedium 45, a coherent light source 50, and a light beam scanning device60.

Here, the hologram recording medium 45 is a medium having the featuresdescribed in Section 1, on which the image 35 of the scatter plate 30 isrecorded. The coherent light source 50 generates a coherent light beamL50 with the same wavelength as the wavelength of light (object lightLobj and reference light Lref) used when creating the hologram recordingmedium 45.

On the other hand, the light beam scanning device 60 bends the lightbeam L50 generated by the coherent light source 50 at the scanningorigin B and irradiates the light beam onto the hologram recordingmedium 45, and scans the light beam by changing the bending mode of thelight beam L50 with time so that the irradiation position of the bentlight beam L60 on the hologram recording medium 45 changes with time.This device is generally known as a scanning mirror device. In thedrawing, for convenience of description, the bending mode at the timingt1 is illustrated by an alternate long and short dashed line, and thebending mode at the timing t2 is illustrated by an alternate long andtwo short dashed line. Specifically, at the timing t1, the light beamL50 is bent at the scanning origin B and irradiated as a light beamL60(t1) onto the point P(t1) of the hologram recording medium 45,however, at the timing t2, the light beam L50 is bent at the scanningorigin B and irradiated as a light beam L60(t2) onto the point P(t2) ofthe hologram recording medium 45.

In the drawing, for convenience of description, only the bending modesat the two timings ti and t2 are shown, however, in actuality, in aperiod from the timing t1 to the timing t2, the bending direction of thelight beam smoothly changes and the irradiation position of the lightbeam L60 on the hologram recording medium 45 gradually moves from thepoint P(t1) to the point P(t2) in the drawing. Specifically, in theperiod from the timing t1 to the timing t2, the irradiation position ofthe light beam L60 is scanned from the point P(t1) to the point P(t2) onthe hologram recording medium 45.

Here, by matching the position of the scanning origin B with theposition of the convergence point C shown in FIG. 4 (in other words, bymaking the position relationship between the hologram recording medium45 and the scanning origin B in FIG. 9 equal to the positionrelationship between the hologram photosensitive medium 40 and theconvergence point C in FIG. 4), on each irradiation position of thehologram recording medium 45, the light beam L60 is irradiated in adirection corresponding to the reference light Lref shown in FIG. 4(direction reversing the optical path of the reference light Lref shownin FIG. 4). Therefore, at each irradiation position of the hologramrecording medium 45, the light beam L60 functions as correctillumination light for reproduction Lrep for reproducing a hologramrecorded there.

For example, at the timing t1, the reproduction image 35 of the scatterplate 30 is produced by the diffracted light L45(t1) from the pointP(t1), and at the timing t2, the reproduction image 35 of the scatterplate 30 is produced by the diffracted light L45(t2) from the pointP(t2). Of course, in the period from the timing tl to t2, thereproduction image 35 of the scatter plate 30 is also produced similarlyby diffracted lights from respective positions onto which the light beamL60 is irradiated. Specifically, as long as the light beam L60 advancesfrom the scanning origin B toward the hologram recording medium 45,whichever position on the hologram recording medium 45 the light beamL60 is irradiated onto, the same reproduction image 35 is produced atthe same position by diffracted light from the irradiation position.

This phenomenon occurs because, as shown in FIG. 4, the image of thescatter plate 30 is recorded as a hologram on the hologram recordingmedium 45 by using the reference light L23 that converges on thespecific convergence point C, and the light beam scanning device 60scans the light beam L60 by using this convergence point C as a scanningorigin B. Of course, even when scanning by the light beam scanningdevice 60 is stopped and the irradiation position of the light beam L60is fixed to a point on the hologram recording medium 45, the samereproduction image 35 is continuously produced at the same position. Thereason why the light beam L60 is scanned in spite of this is forreducing speckle noise.

FIG. 10 is a side view showing a state where an illuminating object 70is illuminated by using the illumination unit 100 shown in FIG. 9. Theillumination unit 100 uses reproduction light of the image 35 of thescatter plate obtained from the hologram recording medium 45 asillumination light. Here, a case where the illuminating object 70 isdisposed at a position at which the left side surface of theilluminating object 70 matches the left side surface of the reproductionimage 35 of the scatter plate as illustrated for illuminating the leftside surface of the illuminating object 70 by the illumination unit 100,is considered. In this case, the left side surface of the illuminatingobject 70 becomes a light receiving surface R, and diffracted light fromthe hologram recording medium 45 is irradiated onto this light receivingsurface R.

Therefore, an arbitrary attention point Q is set on the light receivingsurface R, and diffracted light reaching this attention point Q isconsidered. First, at the timing tl, the light beam L50 output from thecoherent light source 50 is bent at the scanning origin B as illustratedby an alternate long and short dashed line in the drawing, andirradiated as a light beam L60(t1) onto the point P(t1). Then,diffracted light L45(t1) from the point P(t1) reaches the attentionpoint Q. On the other hand, at the timing t2, the light beam L50 outputfrom the coherent light source 50 is bent at the scanning origin B asillustrated by the alternate long and two short dashed line in thedrawing, and irradiated as a light beam L60(t2) onto the point P(t2).Then, diffracted light L45(t2) from the point P(t2) reaches theattention point Q.

Finally, by this diffracted light, at the position of the attentionpoint Q, the reproduction image corresponding to the position of theattention point Q on the scatter plate 30 is always produced, however,the incidence angle of the diffracted light with respect to theattention point Q differs between the timing t1 and the timing t2. Inother words, when the light beam L60 is scanned, although thereproduction image 35 formed on the light receiving surface R does notchange, the incidence angle of diffracted light that reaches therespective points on the light receiving surface R changes with time.This change in incidence angle with time greatly contributes to specklereduction.

As described above, the reason why speckles occur when using coherentlight is because coherent lights reflected by the respective portions ofthe light receiving surface R have extremely high coherence andinterfere with each other. However, in the present invention, byscanning the light beam L60, the incidence angle of the diffracted lightonto each portion of the light receiving surface R changes with time, sothat the interference mode also changes with time and has multiplicity.Therefore, the factor that causes speckles is dispersed temporally, sothat the situation where a spot-like pattern having a physiologicalharmful effect is constantly observed can be eased. This is the basicprinciple of the present invention.

The projection type image display apparatus according to the presentinvention displays an image on a screen by illuminating a spatial lightmodulator by using the illumination unit 100 having the above-describedfeatures. Hereinafter, a description is given of an arrangement andoperations of the projection type image display apparatus with referenceto the plan view shown in FIG. 11.

As shown in FIG. 11, this projection type image display apparatusincludes an illumination unit 100, a spatial light modulator 200, and aprojection optical system 300, and has a function of displaying an imageon a screen 400. The illumination unit 100 is an illumination unit 100shown in FIG. 9 and FIG. 10, and in FIG. 11, the spatial light modulator200 corresponds to the illuminating object 70. In FIG. 9 and FIG. 10,the illumination unit 100 is shown in a side view, however, forconvenience of description, FIG. 11 shows a top view of the projectiontype image display apparatus. Therefore, the illumination unit 100 shownin FIG. 11 is disposed so that the components of the illumination unit100 shown in FIG. 9 and FIG. 10 are in the illustrated state as viewedfrom above.

The spatial light modulator 200 is disposed at a position to be suitablyilluminated by the illumination unit 100. More specifically, theposition relationship between the illumination unit 100 and the spatiallight modulator 200 is adjusted so that a hologram reproduction image 35of the scatter plate 30 is produced at the position at which the spatiallight modulator 200 is disposed. Therefore, the spatial light modulator200 and the reproduction image 35 spatially occupy the same position inspace.

For example, when a transmission type liquid crystal micro-display isused as the spatial light modulator 200, a modulated image is obtainedon the screen of this display. Alternatively, a transmission type LCOS(Liquid Crystal On Silicon) device may be used as the spatial lightmodulator 200. By projecting the modulated image thus obtained onto thescreen 400 by the projection optical system 300, a magnified modulatedimage is displayed on the screen 400. This is the basic operationprinciple of the projection type image display apparatus shown herein.

As the spatial light modulator 200, a reflection type liquid crystalmicro-display or a reflection type LCOS (Liquid Crystal On Silicon)device may be used. In this case, in FIG. 11, the arrangement of thecomponents is changed so that the illumination unit 100 can irradiatelight obliquely onto the spatial light modulator 200 from above in thefigure and reflected light from the spatial light modulator 200 isprojected onto the screen 400 by the projection optical system 300. Whenutilizing such reflected light, a MEMS device such as a DMD (DigitalMicromirror Device) can be used as the spatial light modulator 200.

As described above, a conventional general projection type image displayapparatus using a coherent light source such as a laser poses a problemof the occurrence of speckles on a screen. On the other hand, in theapparatus shown in FIG. 11, speckles that occur on the screen can besignificantly reduced. A first reason for this is that the image of thescatter plate recorded on the hologram recording medium 45 issuperimposed on the position of the spatial light modulator 200 andproduced as a hologram reproduction real image 35, and a second reasonis that this hologram reproduction real image 35 is an image produced bylight beam scanning. Hereinafter, a detailed description is given ofthese reasons.

While the spatial light modulator 200 is a real device such as a liquidcrystal micro-display, a DMD, and an LCOS, the hologram reproductionreal image 35 is an optical reproduction image. Therefore, these can bedisposed to overlap in the same space. Although only the real spatiallight modulator 200 is drawn in FIG. 11, the hologram reproduction realimage 35 of the scatter plate reproduced by the hologram recordingmedium 45 overlaps the real spatial light modulator 200 at the samespatial position.

As a matter of fact, the entity of the hologram reproduction real image35 thus obtained is coherent light diffracted by interference fringesformed on the hologram recording medium 45, and the spatial lightmodulator 200 produces a modulated image while being illuminated by suchcoherent light. For example, when a transmission type liquid crystalmicro-display is used as the spatial light modulator 200, a modulatedimage is obtained as a shading pattern of illumination light transmittedthrough the display.

The projection optical system 300 performs a function of projecting themodulated image thus obtained on the spatial light modulator 200 ontothe screen 400. When a transmission type liquid crystal micro-display isused as the spatial light modulator 200, a modulated image formed onthis display is magnified and projected onto the screen 400, wherebycarrying out image display.

Any projection optical system 300 can be used as long as the opticalsystem has a function of projecting a modulated image obtained on thespatial light modulator 200 onto the screen 400. In the drawing, forconvenience of description, the projection optical system 300 isillustrated as one lens, however, normally, it consists of a pluralityof lenses so as to adjust the focal length. The illustrated example is afront projection type device with which observation is carried out bysetting a viewpoint in front of the screen 400 (the lower side of thescreen 400 in FIG. 11), however, it may also be utilized as a rearprojection type device (that is, a rear projector) with whichobservation is performed by setting a viewpoint on the other side overthe screen 400 (the upper side of the screen 400 in FIG. 11).

Generally, speckles that occur in the projection type image displayapparatus include speckles caused by the illumination light source sideand speckles caused by the screen side. The former are speckles thathave already been included in illumination light on the spatial lightmodulator, and are generated based on a factor of the light source side.On the other hand, the latter are speckles generated by scattering onthe screen.

With the technologies disclosed in Japanese Unexamined PatentPublication No. H06-208089 and Japanese Unexamined Patent PublicationNo. 2004-144936 listed above, illumination light is irradiated by thelight source onto the scatter plate, and by rotary driving oroscillating this scatter plate, speckles on the light source side arereduced. With this method, speckles that are caused by the light sourceside are reduced, however, speckles that are caused by the screen sidecannot be reduced. Further, as described above, this method poses aproblem that a large-scale mechanical drive system is required to rotateor oscillate the scatter plate.

In the present invention, both of the speckles that are caused by thelight source side and speckles that are caused by the screen side can bereduced. First, the reason for reduction in speckles that are caused bythe light source side is because the spatial light modulator 200 isilluminated by the hologram reproduction real image 35 of the scatterplate. A modulated image produced by the spatial light modulator 200 isilluminated by the hologram image 35 of the scatter plate. Originally,respective points of the hologram image 35 are formed of lights fromvarious points of the hologram recording medium 45, so that the lightirradiation angle is multiplexed. Therefore, by adopting the hologramreproduction real image 35 of the scatter plate as an illumination meansfor the spatial light modulator 200, speckles that are caused by thelight source side can be reduced.

The illumination unit 100 used in the present invention obtains thereproduction image 35 by scanning the light beam L60 with respect to thehologram recording medium 45 as shown in FIG. 11, however, in order toreduce speckles that are caused by the light source side, light beamscanning is not always required. Specifically, even when the light beamL60 is kept still and continuously irradiates only one point on thehologram recording medium 45, a reproduction image 35 multiplexed bydiffracted lights from the respective portions of the interferencefringes recorded in the spot region (circular region with a diameter of1 mm in the example shown herein) irradiated with the light beam L60 isproduced, so that an effect of reducing speckles that are caused by thelight source side can be obtained.

Even so, the reason why the light beam L60 is purposely scanned in thepresent invention is for reducing speckles that are caused by the screenside. Hereinafter, a description is given of this with reference to FIG.11.

In FIG. 11, for convenience of description, the optical path of thelight at the timing t1 is illustrated by alternate long and short dashedlines, and the optical path of the light at the timing t2 is illustratedby alternate long and two short dashed lines. Specifically, at thetiming t1, the light beam L50 is bent at a scanning origin B andirradiated as a light beam L60(t1) onto the point P(t1) of the hologramrecording medium 45. Then, based on interference fringes recorded nearthis point P(t1) (inside the spot of the light beam), the reproductionimage 35 of the scatter plate is formed at the position of the spatiallight modulator 200. The light L45(t1) illustrated by alternate, longand short dashed lines in the drawing is diffracted light for formingboth end points E1 and E2 of the reproduction image 35.

This diffracted light L45(t1) is transmitted through the spatial lightmodulator 200, and then passes through the projection optical system300, and is irradiated as projection light L300(t1) onto the screen 400as illustrated by alternate long and short dashed lines in the drawing.The illustrated points G1 and G2 are respectively projection pointscorresponding to both end points E1 and E2 of the reproduction image 35.

Subsequently, behavior of light at the timing t2 is considered. At thetiming t2, the light beam L50 is bent at the scanning origin B, andirradiated as a light beam L60(t2) illustrated by an alternate long andtwo short dashed line onto the point P(t2) of the hologram recordingmedium 45. Then, based on interference fringes recorded near this pointP(t2) (inside the spot of the light beam), the reproduction image 35 ofthe scatter plate is formed at the position of the spatial lightmodulator 200. The light L45(t2) illustrated by alternate long and twoshort dashed lines in the drawing is diffracted light for forming bothend points E1 and E2 of the reproduction image 35.

This diffracted light L45(t2) is transmitted through the spatial lightmodulator 200, and then passes through the projection optical system 300and is irradiated as projection light L300(t2) onto the screen 400 asillustrated by the alternate long and two short dashed lines. Theillustrated points G1 and G2 are respectively projection pointscorresponding to both end points E1 and E2 of the reproduction image 35.As illustrated, the positions of the projection points G1 and G2 at thetiming tl and the positions of the projection points G1 and G2 at thetiming t2 match each other. This is a matter of course by consideringthat the projection optical system 300 is adjusted to magnify andproject the image on the spatial light modulator 200 onto the screen 400and the reproduction image 35 is produced at the position of the spatiallight modulator 200. Specifically, whichever direction the spatial lightmodulator 200 is illuminated from, a magnified image of the spatiallight modulator is formed on the screen 400.

Finally, even when the light beam L60 is scanned by the light beamscanning device 60, the positions of the projection points G1 and G2 onthe screen of both end points E1 and E2 of the reproduction image 35 donot change, and the position that the image on the spatial lightmodulator 200 is magnified and projected onto the screen 400 does notchange either. However, focusing attention on one point on the screen400, the incidence angle of the projection light is multiplexed. This isbecause of the same reason for multiplexing the incidence angle ofdiffracted light reaching the attention point Q shown in FIG. 10.Specifically, a deviation of angle θ1 of the projection point G1 and adeviation of angle θ2 of the projection point G2 occur between theincidence angle of the projection light at the timing t1 and theincidence angle of the projection light at the timing t2.

Thus, by scanning the light beam L60 to be irradiated onto the hologramrecording medium 45, the incidence angle of the projection light thatreaches the respective points on the screen 400 changes with time. Bythus changing the incidence angle with time, the interference modeoccurring on the surface of the screen 400 also changes with time, andhas multiplicity. Therefore, the factor that causes speckles isdispersed temporally, so that the situation where a spot—like patternhaving a physiological harmful effect is constantly observed can beeased. This is the reason for reduction in speckles caused by the screenside.

Thus, the projection type image display apparatus according to thepresent invention can reduce both of the speckles caused by the lightsource side and speckles caused by the screen side. Further, the lightbeam scanning device 60 can be realized by a comparatively small-sizeddevice, so that as compared with a conventional device that rotates oroscillates a scatter plate, the illumination unit 100 can be madesmaller in size and also smaller in power consumption.

<<<Section 3. Detailed Description of Components of Illumination Unit>>>

The illumination unit 100 shown in FIG. 9 includes, as described inSection 2, the hologram recording medium 45, the coherent light source50, and the light beam scanning device 60. Here, a further detaileddescription is given of these components.

<3-1>Coherent Light Source

First, as the coherent light source 50, a light source that generates acoherent light beam L50 with the same wavelength as the wavelength oflight (object light Lobj and reference light Lref) used for creating thehologram recording medium 45 is used. In fact, the wavelength of thelight beam L50 to be generated by the coherent light source 50 does notnecessarily have to be completely equal to the wavelength of the lightused for creating the hologram recording medium 45, and as long as thelight beam has an approximate wavelength, a reproduction image of ahologram can be obtained. In conclusion, the coherent light source 50 tobe used in the present invention is a light source that generates acoherent light beam L50 with a wavelength capable of reproducing theimage 35 of the scatter body.

In actuality, the same light source as the coherent light source 10shown in FIG. 5 can be utilized as it is as the coherent light source50. In the case of the embodiment described herein, a DPSS (Diode PumpedSolid State) laser device capable of emitting laser light with awavelength λ=532 nm (green) was used as the coherent light source 50.The DPSS laser can obtain comparatively high-output laser light with adesired wavelength although the DPSS laser is small in size, so that itis a coherent light source to be suitably utilized for the illuminationunit 100 according to the present invention.

This DPSS laser device has a coherent length longer than that of ageneral semiconductor laser, so that speckles easily occur, andtherefore, the DPSS laser device is conventionally recognized asunsuitable for the illumination purpose. Conventionally, in order toreduce speckles, an effort was made to broaden a range of emissionwavelength of laser and reduce the coherent length as small as possible.On the other hand, in the present invention, even when a light sourcewith a long coherent length is used, due to the above-describedprinciple, occurrence of speckles can be effectively reduced, so thateven when a DPSS laser device is used as a light source, occurrence ofspeckles does not pose a problem in practical use. In this regard, byutilizing the present invention, an effect of widening the selection ofthe light source is obtained.

<3-2>Light Beam Scanning Device

The light beam scanning device 60 is a device having a function ofscanning a light beam on the hologram recording medium 45. Here, adescription is given of a detailed method of beam scanning by this lightbeam scanning device 60. FIG. 12 is a plan view showing a first exampleof a scanning mode of a light beam on the hologram recording medium 45in the illumination unit 100 shown in FIG. 9. In this example, as thehologram recording medium 45, a medium with a lateral width Da=12 mm anda longitudinal width Db=10 mm is used, and as a light beam L60 to scanon the medium, a laser beam having a circular section with a diameter of1 mm is used. As illustrated, a method is adopted in which, in the samemanner as scanning of an electronic beam in a CRT, the irradiationposition of the light beam L60 is scanned in the horizontal directionfrom the start region A1S to the end region A1E of the first line, andthen, scanned in the horizontal direction from the start region A2S tothe end region A2E of the second line . . . , and last, scanned in thehorizontal direction from the start region AnS to the end region AnE ofthe n-th line, and returned to the start region A1S of the first lineagain and repeats the same operation.

With the scanning method shown in FIG. 12, the entire surface of thehologram recording medium 45 is scanned by a light beam, however, in thepresent invention, the entire surface of the hologram recording medium45 does not necessarily have to be completely scanned. For example, FIG.13 shows an example in which only odd-numbered lines are scanned by thescanning method shown in FIG. 12, and scanning of even-numbered lines isomitted. Thus, in the case of scanning on every other line, holograminformation recorded in a region that is a part of the hologramrecording medium 45 does not contribute to image reproduction at all,however, this does not pose any particular problem. FIG. 14 shows anexample of a more extreme scanning method in which scanning on only oneline in the horizontal direction from the start region A1S to the endregion A1E is repeated at the center position of the longitudinal widthDb.

Of course, the scanning direction can be freely set, and after the firstline is scanned from the left to the right, the second line may bescanned from the right to the left. The scanning direction is notnecessarily limited to being straight, and scanning that draws a circleon the hologram recording medium 45 is also possible.

As in the example shown in FIG. 2, when the reference light Lref isirradiated onto and recorded on only the region (hatched region) that isa part of the hologram photosensitive medium 40, no hologram is recordedon the other region (white region on the outer side). In this case, ifthe white region on the outer side is also scanned, the reproductionimage 35 cannot be obtained, so that the illumination becomestemporarily dark. Therefore, in practical use, only the region on whicha hologram is recorded is preferably scanned.

As described above, scanning of a light beam on the hologram recordingmedium 45 is carried out by the light beam scanning device 60. Thislight beam scanning device 60 has a function of bending the light beamL50 from the coherent light source 50 at the scanning origin B(convergence point C when recording a hologram) and irradiating thelight beam onto the hologram recording medium 45. Further, by changingthe bending mode (the bending direction and the amount of the bendingangle) with time, scanning is carried out so that the irradiationposition of the bent light beam L60 onto the hologram recording medium45 changes with time. A device having this function is utilized as ascanning mirror device in various optical systems.

For example, in the example shown in FIG. 9, as the light beam scanningdevice 60, for convenience, a simple reflecting mirror is illustrated,however, in actuality, drive mechanisms that turn this reflecting mirrorin biaxial directions are provided. Specifically, when a scanning originB is set at the center position of the reflecting surface of theillustrated reflecting mirror, and a V axis and a W axis passing throughthis scanning origin B and orthogonal to each other on the reflectingsurface are defined, a mechanism that turns the reflecting mirror aroundthe V axis (axis perpendicular to the paper surface of the drawing) anda mechanism that turns the reflecting mirror around the W axis (axisillustrated by the dashed line in the drawing) are provided.

Thus, by using a reflecting mirror capable of turning around the V axisand the W axis independently, the reflected light beam L60 can bescanned in the horizontal direction and the vertical direction on thehologram recording medium 45. For example, in the above-describedmechanism, by turning the reflected light around the V axis, theirradiation position of the light beam L60 can be scanned in thehorizontal direction on the hologram recording medium 45 shown in FIG.12, and by turning the reflected light around the W axis, theirradiation position can be scanned in the vertical direction.

In conclusion, as long as the light beam scanning device 60 has afunction of bending the light beam L60 so that the light beam swings ona plane including the scanning origin B, the irradiation position of thelight beam L60 can be scanned in a one-dimensional direction on thehologram recording medium 45. As in the example shown in FIG. 14, tooperate the scanning device to scan the light beam only in thehorizontal direction, the light beam scanning device 60 needs to havejust the function of scanning the irradiation position of the light beamin a one-dimensional direction on the hologram recording medium 45.

On the other hand, to operate the scanning device so as to scan theirradiation position of the light beam L60 in two-dimensional directionson the hologram recording medium 45, the light beam scanning device 60is provided with a function of bending the light beam L60 so that thelight beam swings on a first plane including the scanning origin B (inFIG. 9, by turning the reflecting mirror around the V axis, the lightbeam L60 swings on a plane included in the paper surface), and afunction of bending the light beam L60 so that the light beam swings ona second plane that includes the scanning origin B and is orthogonal tothe first plane (in FIG. 9, by turning the reflecting mirror around theW axis, the light beam L60 swings on a plane perpendicular to the papersurface).

As a scanning mirror device for scanning the irradiation position of alight beam in a one-dimensional direction, a polygon mirror is widelyutilized. As a scanning mirror device for scanning the irradiationposition in two-dimensional directions, a pair of polygon mirrors may becombined and used, or devices such as a gimbal mirror, a galvano mirror,and a MEMS mirror are known. Further, other than normal mirror devices,a total reflection prism, a refracting prism, and an electro-opticcrystal (KTN crystal, etc.) or the like can also be utilized as thelight beam scanning device 60.

If the diameter of the light beam L60 becomes close to the size of thehologram recording medium 45, the effect of reducing speckles may belost, so that care must be taken for this. In the example shown in FIG.12 to FIG. 14, as described above, the hologram recording medium 45 hasa lateral width Da=12 mm and a longitudinal width Db=10 mm, and thelight beam L60 is a laser beam having a circular section with a diameterof 1 mm. Under these dimensional conditions, the effect of reducingspeckles is sufficiently obtained. This is because any region on thehologram recording medium 45 is just temporarily irradiated with thelight beam L60, and diffracted light is not continuously output from thesame region.

However, for example, as in the example shown in FIG. 15, when a lightbeam with a diameter close to the size of the hologram recording medium45 is irradiated, a region (hatched region in the drawing) from whichdiffracted light is continuously output is formed. Specifically, evenwhen the irradiation position of the light beam L60 is scanned in thehorizontal direction from the start region A1S to the end region A1E ofthe first line, the hatched region al in the drawing is alwaysirradiated with the light beam. Similarly, even when the irradiationposition is scanned in the horizontal direction from the start regionAnS to the end region AnE of the n-th line, the region a2 is alwaysirradiated with the light beam. In the case of scanning in the verticaldirection, the start regions of the respective lines overlap in theregion a3, and the end regions of the respective lines overlap in theregion a4, so that these regions are always irradiated with the lightbeam even after the line to be scanned is changed.

Eventually, these hatched regions cannot benefit from light beamscanning, and diffracted light is continuously output therefrom. As aresult, diffracted light emitted from such a region is continuouslyincident on the light receiving surface R of the illuminating object atthe same angle, and becomes a factor that causes speckles. Therefore,the diameter of the light beam L60 should not be increased as the sizeof the hologram recording medium 45 gets closer.

This harmful effect also occurs when the scanning pitch is set to besmaller than the diameter of the light beam L60. For example, FIG. 12shows an example in which the scanning pitch in the vertical directionis set to be equal to the diameter of the light beam L60, and FIG. 13shows an example in which the scanning pitch in the vertical directionis set to twice the diameter of the light beam L6O. When the scanningpitch in the vertical direction (vertical scanning direction) is thusset to be equal to or larger than the diameter of the light beam, thescanning region of the i-th line and the scanning region of the (i+1)-thline do not overlap each other, however, if the scanning pitch is lessthan the diameter of the light beam, an overlapping region occurs andmay become a factor that causes speckles as described above.

Moreover, a low scanning speed may also become a factor that causesspeckles. For example, if scanning is carried out at a low speed inwhich it takes an hour to scan one line, in terms of visual timeresolution of humans, this is the same as not scanning, and speckles arerecognized. The reason for speckle reduction by light beam scanning isthat the incidence angle of light to be irradiated onto the respectiveportions of the light receiving surface R is multiplexed by time asdescribed above. Therefore, to sufficiently obtain the speckle reducingeffect by beam scanning, the time during which the same interferenceconditions that causes speckles are maintained is reduced to be shorterthan the visual time resolution of humans.

Generally, the limit of visual time resolution of humans isapproximately 1/20 to 1/30 seconds, and by presenting 20 to 30 frames ormore of still images per second, they are recognized as a smooth movingimage by humans. By taking this into consideration, when the diameter ofthe light beam is represented as d, by carrying out scanning at ascanning speed (speed of 20 d to 30 d per second) for advancing adistance of d or more per 1/20 to 1/30 seconds, a sufficient specklereducing effect is obtained.

<3-3>Hologram Recording Medium

The detailed production process of the hologram recording medium 45 isas described in Section 1 above. Specifically, the hologram recordingmedium 45 to be used in the present invention is a medium that recordsan image of the scatter plate 30 as a hologram by using reference lightthat converges on the specific convergence point C. Therefore, herein, adescription is given of a detailed mode of a hologram recording mediumto be suitably utilized in the present invention.

There are some physical modes of holograms. The inventor of the presentinvention considers that a volume hologram is most preferably utilizedin the present invention. In particular, a volume hologram using aphotopolymer is optimally used.

Generally, a hologram utilized as an anticounterfeit seal on a cash cardand a cash voucher, etc., is called a surface relief (embossed)hologram, and hologram interference fringes are recorded by the surfaceuneven structure. Of course, the hologram recording medium 45 thatrecords the image of the scatter plate 30 as a surface relief hologram(generally called a holographic diffuser) can also be utilized forcarrying out the present invention. However, in the case of this surfacerelief hologram, scattering by the surface uneven structure may become anew factor that causes production of speckles, and therefore, this isnot preferable from the viewpoint of speckle reduction. In the case of asurface relief hologram, multi-order diffracted light is generated, sothat the diffraction efficiency is deteriorated, and further, thediffraction performance (performance that determines how large thediffraction angle can be increased) is also limited.

On the other hand, in the case of a volume hologram, holograminterference fringes are recorded as refractive index distributioninside a medium, so that the hologram is not affected by scattering bythe surface uneven structure. Generally, the diffraction efficiency anddiffraction performance of a volume hologram are better than those of asurface relief hologram. Therefore, when carrying out the presentinvention, a medium that records the image of the scatter plate 30 as avolume hologram is optimally utilized as the hologram recording medium45.

However, even in the case of a volume hologram, if it is of a type thatis recorded by utilizing a photosensitive medium including a silverhalide material, scattering by silver halide particles may become a newfactor that produces speckles, so that it is preferable to avoid use ofthis type. For this reason, the inventor of the present inventionconsiders that a volume hologram using a photopolymer is optimum as thehologram recording medium 45 to be used in the present invention. Adetailed chemical composition of such a volume hologram using aphotopolymer is described in, for example, Japanese Patent No. 2849021.

However, in terms of mass production, a surface relief hologram isbetter than a volume hologram. For a surface relief hologram, anoriginal plate having an uneven structure on the surface is prepared,and by press working by using this original plate, mass production ofmedia is possible. Therefore, when it is demanded to reduce theproduction cost, a surface relief hologram is utilized.

As a physical mode of a hologram, an amplitude modulation hologramformed by recording interference fringes as a shading pattern on a planehas become widely popular. However, this amplitude modulation hologramis low in diffraction efficiency, and light absorption occurs at a darkpattern portion, so that when it is utilized in the present invention,sufficient illumination efficiency cannot be secured. However, in theproduction process thereof, a simple method in which a shading patternis printed on a plane can be adopted, and this is advantageous in termsof production cost. Therefore, an amplitude modulation hologram can alsobe adopted in the present invention depending on the use.

In the recording method shown in FIG. 1, a so-called Fresnel typehologram recording medium is created, however, a hologram recordingmedium of a Fourier transform type obtained by recording the scatterplate 30 through a lens can also be created. In this case, asappropriate, the illumination efficiency may be improved by providing alens on the optical path of the diffracted light L45 to condense light,however, even without a lens, a function as an illumination unit 100 canbe sufficiently performed.

<<<Section 4. Modification of Illumination Unit According to the PresentInvention>>>

A basic embodiment of a projection type image display apparatusaccording to the present invention has been described so far. Thefeature of this basic embodiment is to illuminate a spatial lightmodulator 200 by using a peculiar illumination unit 100 as shown in FIG.9.

When carrying out illumination using the illumination unit 100, first, apreparation step is carried out in which a hologram recording medium 45is created by recording the image 35 of the scatter plate 30 as ahologram on the recording medium 40, and an illumination step is carriedout in which an illumination unit 100 is configured by using thehologram recording medium 45 created in the preparation step, a coherentlight beam L60 is irradiated onto the hologram recording medium 45 in acondition that the spatial light modulator 200 is located at a positionwhere a produced image 35 of the scatter plate 30 is generated, and thislight beam L60 is scanned on the hologram recording medium 45 so thatthe irradiation position changes with time.

In this case, in the preparation step, as shown in FIG. 1, coherentillumination light L12 is irradiated onto the scatter plate 30, andscattered light L30 obtained from the scatter plate 30 is used as objectlight Lobj. Then, coherent light L23 that is irradiated onto therecording medium 40 along a predetermined optical path and has the samewavelength as that of the illumination light L12 is used as referencelight Lref. Then, by recording interference fringes formed by the objectlight Lobj and the reference light Lref on the recording medium 40, thehologram recording medium 45 is created. In the illumination step, asshown in FIG. 9, scanning is carried out so that a light beam L60 withthe same wavelength as that of the reference light Lref (or anapproximate wavelength capable of reproducing a hologram) advancestoward an irradiation position on the hologram recording medium 45 bypassing through an optical path along the optical path of the referencelight Lref (in other words, the light beam L60 is given from a directionoptically conjugate toward the reference light Lref), and reproductionlight of the image 35 of the scatter plate 30, obtained from thehologram recording medium 45, is used as illumination light.

Here, a description is given of several modifications of theabove-described basic embodiment of the illumination unit 100.

<4-1>Hologram Recording Medium on the Assumption of One-DimensionalScanning

In the process of creating the hologram recording medium shown in FIG.1, the parallel light flux L22 is condensed by the convex lens 23 (lenshaving a focal point at the position of the convergence point C) andirradiated as reference light Lref onto the medium 40. Specifically,along a side surface of a cone whose tip is on the convergence point C(theoretically, innumerable cones with radiuses different from eachother are present), the image of the scatter plate 30 is recorded byusing the reference light Lref that three-dimensionally converges on theconvergence point C.

The use of the reference light Lref that three-dimensionally convergesis on the assumption that the light beam L60 is three-dimensionallyscanned (beam is scanned by combining turning around the V axis andturning around the W axis of the reflecting mirror) so that its opticalpath three-dimensionally diverges from the scanning origin B in theillumination unit 100 shown in FIG. 9. Three-dimensional scanning of thelight beam L60 is for two-dimensionally scanning the irradiationposition of the light beam on the hologram recording medium 45 (forscanning in the horizontal direction and scanning in the verticaldirection in FIG. 12).

However, the scanning of the irradiation position of the light beam onthe hologram recording medium 45 does not necessarily have to betwo-dimensionally scanned. For example, in FIG. 14, an example ofscanning of the light beam only in the horizontal direction isillustrated. Thus, on the assumption that the irradiation position ofthe light beam is one-dimensionally scanned, it is rational that thehologram recording medium is also created on the same assumption. Indetail, on the assumption of one-dimensional scanning, instead ofcreating the hologram recording medium 45 as shown in FIG. 14, creatinga band-shaped hologram recording medium 85 shown in FIG. 16 issufficient.

When this hologram recording medium 85 is used, as scanning by the lightbeam scanning device 60, scanning of one line from the start region A1Son the left end to the end region A1E on the right end is repeated. Inthis case, scanning of one line from the left to the right may berepeated, or reciprocatory scanning may be carried out in such a mannerthat scanning from the right to the left is carried out after scanningfrom the left to the right. When the light beam L60 to be used is alaser beam having a circular section with a diameter of 1 mm, thelongitudinal width Db=1 mm of the hologram recording medium 85 shown inFIG. 16 is sufficient. Therefore, as compared with the case where thehologram recording medium 45 shown in FIG. 14 is used, furtherspace-saving is realized, and the apparatus can be downsized as a whole.

The hologram recording medium 85 on the assumption of one-dimensionalscanning can be created by using the optical system shown in FIG. 1,however, instead of this, it may also be created by using the opticalsystem shown in FIG. 17. In the optical system shown in FIG. 17, theconvex lens 23 in the optical system shown in FIG. 1 is replaced by acylindrical lens 24, and the hologram photosensitive medium 40 having arectangular plane is replaced by a hologram photosensitive medium 80having a long and narrow band-shaped plane, and other components are thesame. The lateral width Da of the hologram photosensitive medium 80 isequal to the lateral width of the hologram photosensitive medium 40,however, the longitudinal width Db (width in the direction perpendicularto the paper surface in FIG. 17) is approximate to the diameter of thelight beam (approximately 1 mm in the example described above).

The cylindrical lens 24 is a lens having a columnar surface having acentral axis perpendicular to the paper surface of FIG. 17, and in FIG.17, when a condensing axis passing through the convergence point C andperpendicular to the paper surface is defined, the cylindrical lensperforms a function of condensing the parallel light flux L22 on thecondensing axis. However, due to the properties of the cylindrical lens,light refraction occurs only within a plane parallel to the papersurface, and does not occur in the direction perpendicular to the papersurface. In other words, focusing attention on a plane (paper surface ofFIG. 17) orthogonal to the central axis of the column of the cylindricallens and including the convergence point C, the light L24 thattwo-dimensionally converges along this plane is given as reference lightLref.

Thus, in the present application, “light converges on the convergencepoint C” means not only three-dimensional convergence by the convex lens23 shown in the optical system in FIG. 1, but also two-dimensionalconvergence by the cylindrical lens 24 shown in the optical system inFIG. 17. To create the hologram recording medium 85 on the assumption ofone-dimensional scanning as illustrated in FIG. 16, as shown in theoptical system in FIG. 17, by using a cylindrical lens 24 having acolumnar surface whose central axis is parallel to a condensing axispassing through the convergence point C (axis passing through theconvergence point C and perpendicular to the paper surface in theexample shown in the drawing), a light flux L22 of substantiallyparallel coherent light is condensed on the condensing axis, and byusing light L24 that two-dimensionally converges on the convergencepoint C as reference light Lref, the hologram image of the scatter plate30 is recorded.

<4-2>Hologram Recording Medium Consisting of CGH

The process of creating a hologram recording medium described aboveadopts a pure optical method in which light is actually irradiated ontoa hologram photosensitive medium and interference fringes generatedthere are fixed by chemical change of the photosensitive medium. On theother hand, recently, a method in which this optical process issimulated on a computer, information on interference fringes iscalculated by carrying out an arithmetic operation, and results of thecalculation are fixed onto a medium by a certain physical means, hasbeen established. A hologram created by this method is generally calleda computer generated hologram (CGH).

The hologram recorded on the hologram recording medium used in thepresent invention may be such a computer generated hologram.Specifically, instead of creating a hologram recording medium by theoptical process described in Section 1, a simulation operation usingvirtual object light from a virtual scatter plate and virtual referencelight is carried out to obtain information on interference fringesgenerated on a virtual recording surface, and this information isrecorded on a medium by a physical method, whereby creating a computergenerated hologram.

FIG. 18 is a side view showing the principle of creating a hologramrecording medium as a component of the illumination unit according tothe present invention by means of CGH, and illustrates a method ofsimulating the optical phenomenon shown in FIG. 4 on a computer. Here,the virtual scatter plate 30′ shown in FIG. 18 corresponds to the realscatter plate 30 shown in FIG. 4, and the virtual recording surface 40′shown in FIG. 18 corresponds to the real hologram photosensitive medium40 shown in FIG. 4. The illustrated object light Lobj is virtual lightemitted from the virtual scattered plate 30′, and the illustratedreference light Lref is virtual light with the same wavelength as thatof the object light Lobj. This method is completely the same as themethod described above in that reference light Lref is light thatconverges on the convergence point C. At the respective points on therecording surface 40′, information on interference fringes of thevirtual object light Lobj and reference light Lref is arithmeticallyoperated.

As the virtual scatter plate 30′, for example, a fine three-dimensionalshape model expressed by a polygon, etc., can be used, however, here, asimple model including a large number of point light sources D alignedin a grid pattern on a plane is used. FIG. 19 is a front view of thevirtual scatter plate 30′ shown in FIG. 18, and small white circlesindicate point light sources D, respectively. As illustrated, a largenumber of point light sources D are aligned in a grid pattern at a pitchPa horizontally and a pitch Pb vertically. The pitches Pa and Pb areparameters that determine the surface roughness of the scatter plate.

The inventor of the present invention set the pitches Pa and Pb of thepoint light sources D to approximately the size of 10 μm andarithmetically operated information on interference fringes generated onthe recording surface 40′, and based on the results, formed an unevenpattern on the real medium surface to create a surface relief CGH. Then;when an illumination unit 100 was configured by using this CGH as thehologram recording medium 45, an excellent illumination environment inwhich speckles were reduced was obtained,

FIG. 20 is a table showing experiment results in which a specklereducing effect was obtained by the present invention. Generally, amethod using numerical values called speckle contrasts (unit: %) asparameters showing the degrees of speckles generated on a screen isproposed. The speckle contrast is defined as a numerical value obtainedby dividing the standard deviation in brightness unevenness actuallygenerated on a screen by a brightness average value, when a test patternimage, in which a uniform brightness distribution should normally beobtained, is displayed on the screen. As the speckle contrast valuebecomes larger, the degree of speckle generation on the screen becomeshigher, and a spot-like pattern of brightness unevenness is moreconspicuously presented to an observer.

The table of FIG. 20 shows results of measurement of speckle contrastson the screen 400 illuminated by utilizing the illumination unit 100shown in FIG. 11 and a conventional illumination unit in contrast withthe illumination unit 100, when a test pattern image, in which a uniformbrightness distribution should normally be obtained, is displayed. Themeasurement examples 1 to 3 each show results obtained by using the sameDPSS laser device capable of emitting green laser light as the coherentlight source 50 in the illumination unit 100. A diffusion angle of thehologram recording media used in the measurements (a maximum view anglefrom a point on the hologram recording media toward the reproductionimage 35) is set to 20° in both the examples 2 and 3.

First, the measurement result shown as the measurement example 1 wasobtained by using, instead of the illumination unit 100 shown in FIG.11, a measuring system in which the light beam L50 from the coherentlight source 50 is expanded to become a parallel light flux by the beamexpander and this parallel light flux (laser parallel light) is directlyirradiated onto the spatial light modulator 200. In this case, as shownin the table, a speckle contrast of 20.1% was obtained. This shows astate where a spot-like pattern of brightness unevenness is very clearlyobserved on the screen 400 by the naked eye, which is an unsuitablelevel for practically enjoying image content.

On the other hand, the measurement results shown as measurement examples2 and 3 were both obtained by carrying out illumination by utilizing theillumination unit 100 shown in FIG. 11. Here, the measurement example 2shows a result obtained by utilizing a volume hologram created by anoptical method as the hologram recording medium 45, and the measurementexample 3 shows a result obtained by utilizing a surface relief CGHdescribed above as the hologram recording medium 45. In these results,speckle contrasts lower than 4% were obtained, and this shows anextremely excellent state where a pattern of brightness unevenness ishardly observed by the naked eye (it is generally said that a feeling ofdiscomfort is not given to an observer if the speckle contrast is notmore than 5%). Therefore, in both of the case where a volume hologramcreated by an optical method is utilized and the case where a surfacerelief CGH is utilized as the hologram recording medium 45, apractically satisfactory projection type image display apparatus can beconfigured. The reason why a result (3.0%) better than the result (3.7%)of the measurement result 3 was obtained in the measurement example 2 isconsidered that the resolution of the real scatter plate 30 that becomesthe original image is higher than the resolution of the virtual scatterplate 30′ (a collection of point light sources shown in FIG. 19).

The measurement result shown as the last measurement example 4 wasobtained by using a measuring system in which light from a green LEDlight source is directly irradiated onto the spatial light modulator 200instead of using the illumination unit 100. Originally, an LED lightsource is not a coherent light source, so that it is not necessary toconsider the problem of occurrence of speckles, and as shown in thetable, an excellent result of a speckle contrast of 4.0% was obtained. Areason why the result of the measurement example 4 using incoherentlight is inferior to the results of measurement examples 2 and 3 usingcoherent light is considered that brightness unevenness occurred inlight itself emitted by the LED light source.

<4-3>Display of Color Image

The embodiments described above are examples of projection type imagedisplay apparatuses using a monochromatic laser light source as acoherent light source, and an image obtained on the screen 400 is amonochromatic image corresponding to a color of this laser. However, itis desirable that a general projection type image display apparatus candisplay a color image. Therefore, here, a description is given ofseveral configuration examples of a projection type image displayapparatus capable of presenting a color image. In these examples, thebasic configuration of the portion of the illumination unit is the sameas in the embodiments described above.

(1) FIRST CONFIGURATION EXAMPLE

To present a color image, three primary colors of R (red), G (green),and B (blue) are determined, and respective images in these primarycolors are superimposed and displayed on the screen. In the firstconfiguration example shown here, as the coherent light source 50 in theillumination unit 100 shown in FIG. 11, a light source that produces asynthesized light beam by synthesizing three primary colors of R, G, andB is adopted, and a method for irradiating illumination light includingthree primary color components onto the spatial light modulator 200 isadopted.

FIG. 21 is a configuration view showing an example of such a coherentlight source 50. This device has a function of producing a white lightbeam by synthesizing three primary colors of red, green, and blue.Specifically, a red laser beam L(R) generated by a red laser lightsource 50R and a green laser beam L(G) generated by a green laser lightsource 50G are synthesized by a dichroic prism 15, and further a bluelaser beam L(B) generated by a blue laser light source 50B aresynthesized by a dichroic prism 16, whereby producing a whitesynthesized light beam L (R, G, B).

On the other hand, the light beam scanning device 60 shown in FIG. 11bends the synthesized light beam L (R, G, B) thus produced and scans iton the hologram recording medium 45. On the hologram recording medium45, the image 35 of the scatter plate 30 is recorded in advance as threeholograms by using lights with the same wavelengths (or approximatewavelengths) as those of the laser beams L(R), L(G), and L(B) generatedby the above-described three laser light sources 50R, 50G, and 50B.Accordingly, from the hologram recording medium 45, diffracted lights ofthe R, G, and B color components are obtained, and reproduction images35 of the R, G, and B color components are produced at the sameposition, and accordingly, a white reproduction image is obtained.

To create a hologram recording medium on which the image of the scatterplate 30 is recorded by using lights in three colors of R, G, and B, aprocess of recording holograms by using, for example, a hologramphotosensitive medium on which a pigment photosensitive to light in Itcolor, a pigment photosensitive to light in G color, and a pigmentphotosensitive to light in B color are uniformly distributed, and thesynthesized light beam L

(R, G, B). Alternatively, a hologram photosensitive medium having athree-layer structure including lamination of a first photosensitivelayer photosensitive to light in R color, a second photosensitive layerphotosensitive to light in G color, and a third photosensitive layerphotosensitive to light in B color may be used. Alternatively, it isalso possible that the three photosensitive layers are prepared asseparate media, and holograms are recorded thereon by using lights incorresponding colors separately, and last, these three layers are stucktogether to compose a hologram recording medium having a three-layerstructure.

Finally, to the spatial light modulator 200 shown in FIG. 11,illumination light including R, G, and B color components is supplied.Therefore, the spatial light modulator 200 is provided with a functionof modulating light on a pixel basis independently by defining a pixelarray spatially disposed and assigning any of the three primary colorsR, G, and B to each of the pixels. For example, the spatial lightmodulator 200 shown at the left in FIG. 22 is an example in which atwo-dimensional pixel array is defined on a plane, and pixels of thethree primary colors It, G, and B are uniformly distributed. When thisspatial light modulator 200 consists of, for example, a liquid crystaldisplay, the illustrated pixels function as elements capable ofcontrolling transmittancy independently by means of liquid crystalorientation.

On the other hand, a color filter 250 as shown at the right in FIG. 22is superimposed on the spatial light modulator 200. The color filter 250is a filter having the same size as that of the spatial light modulator200, on which exactly the same pixel array as that defined on thespatial light modulator 200 is defined. In addition, at the positions ofthe pixels on the color filter 250, filters of primary colorscorresponding to the pixels at the same positions on the spatial lightmodulator 200 are provided. Specifically, in FIG. 22, a filter thattransmits the primary color It is provided on each pixel R on the colorfilter 250, a filter that transmits the primary color G is provided oneach pixel G, and a filter that transmits the primary color B isprovided on each pixel B.

By supplying illumination light including R, G, and B color componentsin the state where the color filter 250 is superimposed on the spatiallight modulator 200, only the component of the primary color R istransmitted through the pixels to which the primary color R is assigned,only the component of the primary color G is transmitted through thepixels to which the primary color G is assigned, only the component ofthe primary color B is transmitted through the pixels to which theprimary color B is assigned. Accordingly, on the screen 400, a colorimage formed on the spatial light modulator 200 is displayed, so that aprojection type image display apparatus having a color image displayfunction is realized.

(2) SECOND CONFIGURATION EXAMPLE

In a second configuration example for displaying a color image, anillumination unit and a spatial light modulator are prepared for eachprimary color, and finally, images in the primary colors are synthesizedand projected onto the screen by a projection optical system.

FIG. 23 is an arrangement drawing showing this second configurationexample. In this second configuration example, basically, componentsshown in FIG. 11 except for the projection optical system 300 areprepared for each of the three primary colors It, G, and B, modulatedimages of the three primary colors It, G, and B are producedindependently, and synthesized and projected onto the screen 400. Thecross dichroic prism 350 shown at the center in FIG. 23 is a componentof the projection optical system in a broad sense, and has a function ofsynthesizing modulated images of three primary colors R, G, and B. Theimage thus synthesized is projected onto the screen 400 by theprojection optical system 300.

In FIG. 23, the first spatial light modulator 200R is a spatial lightmodulator that carries out modulation based on a first image having acomponent of the first primary color R, and the first illumination unit100R is a unit that supplies first illumination light with a wavelengthcorresponding to the first primary color It to the first spatial lightmodulator 200R.

Similarly, the second spatial light modulator 200G is a spatial lightmodulator that carries out modulation based on a second image having acomponent of the second primary color G, and the second illuminationunit 100G is a unit that supplies second illumination light with awavelength corresponding to the second primary color G to the secondspatial light modulator 200G.

A1so, the third spatial light modulator 200B is a spatial lightmodulator that carries out modulation based on a third image having acomponent of the third primary color B, and the third illumination unit100B is a unit that supplies third illumination light with a wavelengthcorresponding to the third primary color B to the third spatial lightmodulator 200B.

The basic configurations of the spatial light modulators 200R, 200G, and200B are the same as the configuration of the spatial light modulator200 according to the basic embodiment described above except only thatthe spatial light modulators 200R, 200G, and 200B modulate light basedon image information on the primary colors different from each other.The basic configurations of the illumination units 100R, 100G, and 100Bare also the same as the configuration of the illumination unit 100according to the basic embodiment described above except only that theillumination units 100R, 100G, and 100B have coherent light sources thatgenerate laser beams of the primary colors different from each other.

Finally, a projection optical system in a broad sense consisting of thecross dichroic prism 350 and the projection optical system 300 guidesillumination light modulated by the first spatial light modulator 200R,illumination light modulated by the second spatial light modulator 200G,and illumination light modulated by the third spatial light modulator200B to the screen 400, and superimposes and projects a first image in Rcolor, a second image in G color, and a third image in B color onto thescreen 400.

Accordingly, on the screen 400, a color image is displayed.

(3) THIRD CONFIGURATION EXAMPLE

A third configuration example described here is a compromise between theabove-described first configuration example and second configurationexample, in which the illumination units 100R, 100G, and 100B in thesecond configuration example shown in FIG. 23 are replaced by theillumination unit in the first configuration example using a lightsource that generates a synthesized light beam L (R, G, B) shown in FIG.21.

Specifically, the first spatial light modulator 200R, the second spatiallight modulator 200G, and the third spatial light modulator 200B, thecross dichroic prism 350, and the projection optical system 300 shown inFIG. 23 are left as they are, and as an illumination unit, only onecommon illumination unit (unit using the coherent light source 50 thatproduces a synthesized light beam L (R, G, B) shown in FIG. 21) is used.

Thus, the illumination unit is commonly used, so that a little ingenuityis required. Specifically, inside the common illumination unit 100, thelight beam scanning device 60 scans the synthesized light beam L (R, G,B) on the hologram recording medium 45, and therefore, the image 35 ofthe scatter plate 30 is recorded as three holograms on the hologramrecording medium 45 by using lights with the same wavelengths (orapproximate wavelengths) as those of the laser beams generated by thethree laser light sources 50R, 50G, and 50B shown in FIG. 21 (as in thefirst configuration example described above).

The common illumination unit 100 is further provided with a switchingdevice that performs time-division supplying operations so as to supplyillumination light obtained from the hologram recording medium 45 to thefirst spatial light modulator 200R in a first period, supply theillumination light to the second spatial light modulator 200G in asecond period, and supply the illumination light to the third spatiallight modulator 200B in a third period. This switching device canconsist of, for example, a movable reflecting mirror.

On the other hand, the components shown in FIG. 21 are configured tointermittently operate so that the first laser light source 50Rgenerates a first laser beam L(R) in the first period, the second laserlight source 50G generates a second laser beam L(G) in the secondperiod, and the third laser light source 50B generates a third laserbeam L(B) in the third period.

Accordingly, in the first period, only the first laser beam L(R) isirradiated from the coherent light source 50 and supplied to the firstspatial light modulator 200R. In the second period, only the secondlaser beam L(G) is irradiated from the coherent light source 50 andsupplied to the second spatial light modulator 200G. In the thirdperiod, only the third laser beam L(B) is irradiated from the coherentlight source 50 and supplied to the third spatial light modulator 200B.Therefore, operations equivalent to the operations in theabove-described second configuration example can be carried out althoughthe operations are time-divisional operations.

(4) FOURTH CONFIGURATION EXAMPLE

In a fourth configuration example described last, one spatial lightmodulator 200 is commonly used as the first to third spatial lightmodulators 200R, 200G, and 200B used in the third configuration exampledescribed above. In this case, of course, the cross dichroic prism 350becomes unnecessary. To commonly use the spatial light modulator 200,this common spatial light modulator 200 is made to carry outtime-divisional operations. Specifically, the spatial light modulator200 carries out time-divisional modulating operations to carry outmodulation based on a first image having a first primary color componentR in the first period, carry out modulation based on a second imagehaving a second primary color component G in the second period, andcarry out modulation based on a third image having a third primary colorcomponent B in the third period.

On the other hand, the coherent light source includes, as in the thirdconfiguration example, as shown in FIG. 21, a first laser light source50R that generates a first laser beam L(R) with a wavelengthcorresponding to the first primary color R, a second laser light source50G that generates a second laser beam L(G) with a wavelengthcorresponding to the second primary color G, a third laser light source50B that generates a third laser beam L(B) with a wavelengthcorresponding to the third primary color B, and light synthesizers 15and 16 that produce a synthesized light beam L (R, G, B) by synthesizinglaser beams generated by these three laser light sources.

The light beam scanning device 60 scans the synthesized light beam L (R,G, B) produced by the light synthesizers 15 and 16 on the hologramrecording medium 45. The image 35 of the scatter plate 30 is recorded asthree holograms on the hologram recording medium 45 by using lights withthe same wavelengths (or approximate wavelengths) as those of the laserbeams generated by the three laser light sources 50R, 50G, and 50B shownin FIG. 21 (as in the first and third configuration examples describedabove). However, unlike the third configuration example, the spatiallight modulator 200 is singular, so that illumination light obtainedfrom the hologram recording medium 45 is directly supplied to thissingle spatial light modulator 200.

Then, as in the third configuration example, components shown in FIG. 21are configured to intermittently operate so that the first laser lightsource 50R generates the first laser beam L(R) in the first period, thesecond laser light source 50G generates the second laser beam L(G) inthe second period, and the third laser light source 50B generates thethird laser beam L(B) in the third period.

Accordingly, in the first period, only the first laser beam L(R) isirradiated from the coherent light source 50, and the spatial lightmodulator 200 that received illumination light of R color based on thisirradiation carries out modulation based on a first image having thefirst primary color component R. In the subsequent second period, onlythe second laser beam L(G) is irradiated from the coherent light source50, and the spatial light modulator 200 that received illumination lightof G color based on this irradiation carries out modulation based on asecond image having the second primary color component G. Then, in thethird period, only the third laser beam L(B) is irradiated from thecoherent light source 50, and the spatial light modulator 200 thatreceived illumination light of B color based on this irradiation carriesout modulation based on a third image having the third primary colorcomponent B. Accordingly, color image display is possible althoughoperations are time-divisional operations.

<4-4>Geometric Variation for Creating Hologram Recording Medium

In Section 1, a method for recording a hologram image of the scatterplate 30 on the hologram photosensitive medium 40 is described withreference to FIG. 1. This method is a method for creating a reflectiontype hologram recording medium by using reference light that convergeson the convergence point C, and the geometric arrangement of necessarycomponents is as shown in the side view of FIG. 24.

In the example shown in FIG. 24, the convergent reference light Lrefadvancing toward the convergence point C is produced by the convex lens23, and the medium 40 is disposed between the convex lens 23 and theconvergence point C. The medium 40 is disposed obliquely as illustrated,and onto the lower surface side thereof, object light Lobj from thescatter plate 30 is irradiated. The hologram recording medium created bythis method becomes a reflection type medium. Specifically, whencarrying out reproduction, as shown in FIG. 25, a light beam thatfunctions as illumination light for reproduction Lrep is irradiated ontothe lower surface side of the medium 45, and the reproduction image 35is produced by reflected diffracted light Ldif from the point P.

Thus, in the examples described above, a hologram recorded on thehologram recording medium 45 is a reflection type hologram, andreflected diffracted light of a light beam is used as illuminationlight. On the other hand, it is also possible that a hologram recordedon the hologram recording medium 45 is a transmission type hologram, andtransmitted diffracted light of the light beam is used as illuminationlight.

FIG. 26 is a side view showing geometric arrangement when creating sucha transmission type hologram. The difference from the arrangement shownin FIG. 24 is the orientation of the medium 40. In the method forcreating a reflection type hologram shown in FIG. 24, reference lightLref is irradiated onto the upper surface of the medium, and objectlight Lobj is irradiated onto the lower surface of the medium. By thusirradiating the reference light and the object light onto surfaces onthe sides opposite to each other, a reflection type hologram can berecorded. On the other hand, in the method shown in FIG. 26, both of thereference light Lref and the object light Lobj are irradiated onto theupper surface of the medium 40. Thus, by irradiating reference light andobject light from the same side, a transmission type hologram can berecorded. Specifically, when carrying out reproduction, as shown in FIG.27, a light beam functioning as illumination light for reproduction Lrepis irradiated onto the lower surface side of the medium 45, and thereproduction image 35 is produced by transmitted diffracted light Ldiffrom the point P.

Although the examples described above are methods for creating areflection type or transmission type hologram recording medium by usingreference light that converges on the convergence point C, a reflectiontype or transmission type hologram recording medium can also be createdby using reference light that diverges from the convergence point Cinstead. However, in this case, a preparatory hologram recording mediummust be created in advance. Hereinafter, a description is given ofprocesses for carrying out this method in order.

First, as shown in FIG. 28, the preparatory hologram photosensitivemedium 90 and the scatter plate 30 are disposed, and parallel referencelight Lref is irradiated onto the medium 90 obliquely from the upperright as illustrated. Then, interference fringes generated by the objectlight Lobj from the scatter plate 30 and the reference light Lref arerecorded on the medium 90. Thus, when carrying out recording, byirradiating object light and reference light from the same side, atransmission type hologram is recorded. Here, the medium 90 onto which ahologram is thus recorded is referred to as a preparatory hologramrecording medium 95.

FIG. 29 is a side view showing a reproduction process of the preparatoryhologram recording medium 95. As illustrated, when parallel illuminationlight for reproduction Lrep is irradiated obliquely onto the medium 95from the lower left, by transmitted diffracted light Ldif, thereproduction image 35 is produced on the right side in the drawing.Here, the extension of the direction of the illumination light forreproduction Lrep matches the direction of the reference light Lrefshown in FIG. 28, and the production position of the reproduction image35 matches the position at which the scatter plate 30 is disposed shownin FIG. 28.

Subsequently, a process of recording an image of the scatter plate 30 onthe hologram photosensitive medium 40 by using the reproduction image 35generated by the preparatory hologram recording medium 95 as asubstitute for the real scatter plate 30 is carried out. Specifically,as shown in FIG. 30, the hologram photosensitive medium 40 is disposedon the right side of the preparatory hologram recording medium 95, andby irradiating parallel illumination light for reproduction Lrep ontothe medium 95 obliquely from the lower left, the reproduction image 35is produced on the right side in the drawing. In this case, the lightemitting rightward from the medium 95 is transmitted diffracted lightLdif for reproducing the reproduction image 35 and at the same time,functions as object light Lobj for the medium 40.

On the other hand, from the lower side in the drawing, divergentreference light Lref is irradiated onto the medium 40. This divergentreference light Lref is light diverging from the convergence point C(when a point light source is present on the convergence point C, lightoutput from this point light source), and a bundle of rays diffusing ina conical shape is irradiated onto the medium 40. In the illustratedexample, by producing a point light source by condensing the parallellight flux L10 on the convergence point C by the convex lens 25 having afocal point at the position of the convergence point C, divergentreference light Lref is generated. By using, for example, a microlenswith a diameter of approximately 1 mm as the convex lens 25, divergentreference light Lref can be generated by utilizing a laser beam with asectional diameter of approximately 1 mm output from the laser lightsource as the parallel light flux L10.

In the method shown in FIG. 30, the object light Lobj is irradiated ontothe upper surface of the medium 40, and the reference light Lref isirradiated onto the lower surface of the medium 40. By thus irradiatingreference light and object light onto surfaces on the sides opposite toeach other, a reflection type hologram can be recorded. Therefore, thehologram recording medium 45 created by the method shown in FIG. 30 issubstantially the same reflection type hologram as the hologramrecording medium 45 created by the method shown in FIG. 24. Therefore,when carrying out reproduction, the geometric arrangement shown in FIG.25 is adopted.

On the other hand, FIG. 31 is a side view showing an example in which atransmission type hologram is created by using divergent reference lightLref. The difference from the arrangement shown in FIG. 30 is theorientation of the medium 40. In the method for creating a reflectiontype hologram shown in FIG. 30, the object light Lobj is irradiated ontothe upper surface of the medium, and the reference light Lref isirradiated onto the lower surface of the medium. On the other hand, inthe method shown in FIG. 31, both of the object light Lobj and thereference light Lref are irradiated onto the lower surface of the medium40. By thus irradiating reference light and object light from the sameside, a transmission type hologram can be recorded. The hologramrecording medium 45 created by the method shown in FIG. 31 issubstantially the same transmission type hologram as the hologramrecording medium 45 created by the method shown in FIG. 26. Therefore,when carrying out reproduction, the geometric arrangement shown in FIG.27 is adopted.

In the recording processes shown in FIG. 30 and FIG. 31, thetransmission type hologram created by the method shown in FIG. 28 isused as the preparatory hologram recording medium 95, however, thereflection type hologram created by the method shown in FIG. 32 may alsobe used as the preparatory hologram recording medium 95. In the methodshown in FIG. 32, reference light Lref is irradiated onto thepreparatory hologram photosensitive medium 90 from the left side, andobject light Lobj is irradiated from the right side, so that the createdpreparatory hologram recording medium 95 is a reflection type hologram.

When carrying out reproduction by using this reflection type preparatoryhologram recording medium 95, as shown in FIG. 33, illumination lightfor reproduction Lrep is irradiated onto the medium 95 from the rightside, and the reproduction image 35 is produced by the obtainedreflected diffracted light Ldif. Therefore, in the process shown in FIG.30 and FIG. 31, the illumination light for reproduction Lrep isirradiated from the right side instead of from the left side.

<4-5>Parallel-Moving Scanning of Light Beam

In the embodiments described above, a method in which the light beamscanning device 60 in the illumination unit 100 bends a light beam at ascanning origin B and scans the bent light beam by changing the bendingmode (bending direction and the amount of the bending angle) with timeis adopted. However, the scanning method of the light beam scanningdevice 60 is not limited to the method in which a light beam is bent atthe scanning origin B.

For example, a scanning method in which a light beam is moved parallelcan also be adopted. However, in this case, the method for recording thescatter plate 30 on the hologram recording medium 45 must also bechanged. Specifically, as in the example shown in FIG. 34, referencelight Lref composed of a parallel light flux is irradiated onto thehologram photosensitive medium 40, and information on interferencefringes formed by interference with object light Lobj from the scatterplate 30 is recorded, In other words, on the hologram recording medium46 thus created, the image 35 of the scatter plate 30 is recorded as ahologram by using the reference light Lref composed of a parallel lightflux.

FIG. 35 is a side view of an illumination unit 110 using the hologramrecording medium 46 created by the method shown in FIG. 34. Asillustrated, this illumination unit 110 includes the hologram recordingmedium 46, the coherent light source 50, and the light beam scanningdevice 65.

Here, the hologram recording medium 46 is a medium created by the methodshown in FIG. 34, on which the image 35 of the scatter plate 30 isrecorded as a hologram by utilizing reference light Lref composed of aparallel light flux. The coherent light source 50 is a light source thatgenerates a coherent light beam L50 with the same wavelength (or anapproximate wavelength capable of reproducing a hologram) as thewavelength of light (object light Lobj and reference light Lref) usedfor creating the hologram recording medium 46.

On the other hand, the light beam scanning device 65 has a function ofirradiating the light beam L50 generated by the coherent light source 50onto the hologram recording medium 46, and at this time, carries outscanning so that the light beam L65 is irradiated onto the hologramrecording medium 46 from a direction parallel to the reference lightLref used in the creating process shown in FIG. 34. In detail, scanningis carried out so that the light beam L65 is irradiated onto thehologram recording medium 46 while being moved parallel so that theirradiation position of the light beam L65 on the hologram recordingmedium 46 changes with time.

The light beam scanning device 65 that carries out scanning in thismanner can consist of, for example, a movable reflecting mirror 66 and adrive mechanism that drives the movable reflecting mirror 66.Specifically, as shown in FIG. 35, a movable reflecting mirror 66 isdisposed at a position at which the movable reflecting mirror canreceive the light beam L50 generated by the coherent light source 50,and a drive mechanism that slides the movable reflecting mirror 66 alongthe optical axis of the light beam L50 is provided. In practical use,the light beam scanning device 65 having a function equivalent to thefunction described above can consist of a micromirror device utilizing aMEMS. Alternatively, also by making the light beam L60 bent at theposition of the scanning origin B by the light beam scanning device 60shown in FIG. 9 pass through a convex lens having a focal point on thescanning origin B, a light beam that moves parallel can also beproduced.

In the example shown in FIG. 35, the hologram recording medium 46irradiated with the light beam L65 reflected by the movable reflectingmirror 66 generates diffracted light based on recorded interferencefringes, and by this diffracted light, the reproduction image 35 of thescatter plate 30 is produced. The illumination unit 110 carries outillumination by utilizing the reproduction light thus obtained of thereproduction image 35 as illumination light.

In FIG. 35, for convenience of description, the position of the lightbeam at the timing t1 is illustrated by an alternate long and shortdashed line, and the position of the light beam at the timing t2 isillustrated by an alternate long and two short dashed line.Specifically, at the timing t1, the light beam L50 is reflected at theposition of the movable reflecting mirror 66(t1), and irradiated as alight beam L65(t1) onto the point P(t1) of the hologram recording medium46. On the other hand, at the timing t2, the light beam L50 is reflectedat the position of the movable reflecting mirror 66(t2) (the illustratedmovable reflecting mirror 66(t2) is the movable reflecting mirror 66(t1)after it moved), and irradiated as a light beam L65(t2) onto the pointP(t2) of the hologram recording medium 46.

In the drawing, for convenience, only scanning modes at the two timingst1 and t2 are shown, however, in actuality, in the period from thetiming t1 to t2, the light beam L65 moves parallel in the left-rightdirection in the drawing and the irradiation position of the light beamL65 on the hologram recording medium 46 gradually moves from the pointP(t1) to P(t2) in the drawing. Specifically, in the period from thetiming t1 to t2, the irradiation position of the light beam L65 isscanned from the point P(t1) to P(t2) on the hologram recording medium46. Here, an example in which the light beam L65 is moved parallel in aone-dimensional direction (the left-right direction in the drawing) isdescribed, and of course, by providing a mechanism that moves the lightbeam L65 parallel in a direction perpendicular to the paper surface ofthe drawing as well (for example, a mechanism including a reflectingmirror disposed on the XY stage), the light beam can be moved parallelin two-dimensional directions.

Here, the light beam L65 is scanned so as to become always parallel tothe reference light Lref used in the creating process shown in FIG. 34,so that at each irradiation position on the hologram recording medium46, the light beam L65 functions as correct illumination light forreproduction Lrep for reproducing a hologram recorded there.

For example, at the timing t1, the reproduction image 35 of the scatterplate 30 is produced by diffracted light L46(t1) from the point P(t1),and at the timing t2, the reproduction image 35 of the scatter plate 30is produced by diffracted light L46 (t2) from the point P(t2). Ofcourse, in the period from the timing t1 to t2, by diffracted lightsfrom the respective positions onto which the light beam L65 isirradiated, the reproduction image 35 of the scatter plate 30 is alsoproduced in the same manner. Specifically, as long as the light beam L65is scanned to move parallel, whichever position on the hologramrecording medium 46 the light beam L65 is irradiated onto, the samereproduction image 35 is produced at the same position by diffractedlight from the irradiation position.

Finally, the illumination unit 110 shown in FIG. 35 has a function toilluminate the spatial light modulator 200 by the reproduction image 35in the same manner as in the illumination unit 100 shown in FIG. 9. Inconclusion, in the present invention, an image of the scatter plate isrecorded as a hologram on a hologram recording medium by using referencelight irradiated along an optical path, and by the light beam scanningdevice, a light beam is scanned so that the irradiation direction of thelight beam onto the hologram recording medium is along (opticallyconjugate toward) the optical path of the reference light.

<4-6>Utilization of Microlens Array

In the embodiments described above, a hologram recording medium on whicha hologram image of the scatter plate 30 is recorded is prepared, acoherent light is scanned on the hologram recording medium, and obtaineddiffracted light is utilized as illumination light. Here, a descriptionis given of a modification utilizing a microlens array instead of thehologram recording medium.

FIG. 36 is a side view of the modification utilizing a microlens array.An illumination unit 120 according to the present modification includesa microlens array 48, a coherent light source 50, and a light beamscanning device 60. The coherent light source 50 generates a coherentlight beam L50 as in the embodiments described above, and specifically,a laser light source can be used.

The light beam scanning device 60 scans the light beam L50 generated bythe coherent light source 50 as in the embodiments described above. Morespecifically, the light beam scanning device has a function of bendingthe light beam at the scanning origin B and irradiating it onto themicrolens array 48, and in addition, carries out scanning by changingthe bending mode of the light beam L50 with time so that the irradiationposition of the light beam L60 on the microlens array 48 changes withtime.

On the other hand, the microlens array 48 is an optical elementconsisting of a collection of a large number of independent lenses. Eachof the independent lenses constituting the microlens array 48 has afunction of refracting light incident from the scanning origin B andforming an irradiation region I on the light receiving surface R of thespatial light modulator 200 located at a particular position. Further,the independent lenses are configured so that all irradiation regions Iformed by the independent lenses become the same common region on thelight receiving surface R. As a microlens array having this function,for example, a microlens array called “fly-eye lens” is commerciallyavailable.

FIG. 37 is a side view showing an operation principle of theillumination unit 120 shown in FIG. 36. A1so here, for convenience ofdescription, the bending mode at the timing t1 of the light beam L60 isillustrated by an alternate long and short dashed line, and the bendingmode at the timing t2 is illustrated by an alternate long and two shortdashed line. Specifically, at the timing tl, the light beam L50 is bentat the scanning origin B, and incident as a light beam L60(t1) on theindependent lens 48-1 positioned on the lower side of the microlensarray 48. This independent lens 48-1 has a function of expanding thelight beam incident from the scanning origin B and irradiating the lightbeam onto a two-dimensional irradiation region I on the light receivingsurface R of the spatial light modulator 200. Therefore, on the lightreceiving surface R of the spatial light modulator 200, the irradiationregion I is formed as illustrated.

At the timing t2, the light beam L50 is bent at the scanning origin B,and incident as a light beam L60(t2) on the independent lens 48-2positioned on the upper side of the microlens array 48. This independentlens 48-2 has a function of expanding the light beam incident from thescanning origin B and irradiating the light beam onto thetwo-dimensional irradiation region I on the light receiving surface R ofthe spatial light modulator 200. Therefore, at the timing t2, theirradiation region I is also formed on the light receiving surface R ofthe spatial light modulator 200 as illustrated.

In the drawing, only operation states at the timings t1 and t2 areshown, however, in actuality, in the period from the timing t1 to t2,the bending direction of the light beam smoothly changes, and theirradiation position of the light beam L60 on the microlens array 48gradually moves from the lower side to the upper side in the drawing.Specifically, in the period from the timing t1 to t2, the irradiationposition of the light beam L60 is scanned up and down on the microlensarray 48. Of course, when a microlens array 48 including a large numberof independent lenses arrayed two-dimensionally is used, the light beamis scanned on this two-dimensional array by the light beam scanningdevice 60.

Due to the above-described properties of the microlens array 48,whichever independent lens the light beam L60 is incident on, thetwo-dimensional irradiation region I formed on the light receivingsurface R is common. That is, regardless of the light beam scanningstate, the same irradiation region I is always formed on the lightreceiving surface R. Therefore, when a light modulating plane of thespatial light modulator 200 (for example, a display surface plane incase of a liquid crystal micro-display being used as the spatial lightmodulator 200) is located so as to be positioned in the irradiationregion I, the light modulating plane becomes a state where illuminationlight is always irradiated and it becomes possible to project the imageon a screen.

In fact, in practical use, even when the irradiation regions I generatedby the independent lenses are not completely the same but slightlydeviate from each other, this does not pose a problem in obtaining aprojected image on a screen, as far as such a state is maintained thatat least an inside region of the light modulating plane is alwaysirradiated by illumination light.

Finally, in the case of the illumination unit 120 shown herein, thelight beam scanning device 60 has a function of irradiating the lightbeam L60 onto the microlens array 48 and scanning the light beam L60 sothat the irradiation position of the light beam L60 on the microlensarray 48 changes with time. On the other hand, each of the independentlenses constituting the microlens array 48 has a function of refractinglight irradiated from the light beam scanning device 60 and forming theirradiation regions I on the light receiving surface It of the spatiallight modulator 200, and is configured so that all irradiation regions Iformed by the independent lenses become substantially the same commonregion on the light receiving surface R.

In this illumination apparatus 120, as in the illumination unit 100according to the basic embodiment described above, the incidence angleof light to be irradiated onto each portion of the light receivingsurface R is multiplexed by time, Therefore, occurrence of specklescaused by the illumination light source side is reduced. Further,occurrence of speckles caused by the screen side is also reduced becausea light beam L60 is scanned.

<4-7>Utilization of Optical Diffusing Element

An example of an illumination unit configured by using a hologramrecording medium on which a hologram image of the scatter plate 30 isrecorded is described above as a basic embodiment, and in <4-6>describedabove, an example of an illumination unit configured by using amicrolens array instead of a hologram recording medium is described. Inthese illumination units, ultimately, the hologram recording medium andthe microlens array perform the role of an optical diffusing elementhaving a function of forming irradiation regions on a light receivingsurface by diffusing an incident light beam. In addition, the opticaldiffusing element has a feature that the formed irradiation regionsbecome the same common region on the light receiving surface regardlessof the incidence positions of the light beam.

Therefore, to configure an illumination unit used for a projection typeimage display apparatus according to the present invention, theabove-described hologram recording medium and microlens array do notnecessarily have to be used, and generally, the illumination apparatuscan be configured by using an optical diffusing element having theabove-described feature.

In conclusion, the illumination unit used for a projection type imagedisplay apparatus according to the present invention can be essentiallyconfigured by using a coherent light source that generates a coherentlight beam, a light beam scanning device that carries out beam scanningby controlling either or both of the direction and position of the lightbeam, and an optical diffusing element that diffuses the incident lightbeam and emits it.

Here, the light beam scanning device is sufficient as long as it has afunction of guiding a light beam generated by the coherent light sourcetoward the optical diffusing element and scanning the guided light beamso that the incidence position of the light beam on the opticaldiffusing element changes with time. The optical diffusing element issufficient as long as it has a function of forming irradiation regionson a light receiving surface of the spatial light modulator 200 bydiffusing the incident light beam, and be configured so that the formedirradiation regions become substantially the same common region on thelight receiving surface regardless of incidence positions of theincident light beam.

INDUSTRIAL APPLICABILITY

A projection type image display apparatus according to the presentinvention can be widely utilized in the industry as an apparatus toproject and display various types of images, not only still images butalso motion images, on a screen.

1.-31. (canceled)
 32. An optical module comprising: a light beamscanning device that carries out beam scanning by controlling either orboth of a direction and a position of a given coherent light beam, andan optical diffusing element that diffuses an incident light beam andemits light, wherein the light beam scanning device guides said givencoherent light beam toward the optical diffusing element, and carriesout scanning so that both an incidence position and an incidencedirection of the guided light beam on the optical diffusing elementchanges with time, and the optical diffusing element has a function offorming irradiation regions on a light receiving surface by diffusing anincident light beam, and is configured so that the formed irradiationregions become substantially a same common region on the light receivingsurface regardless of an incidence position of the incident light beamand diffused light from the optical diffusing element directly reachesthe light receiving surface without passing any optical system.
 33. Theoptical module according to claim 32, wherein the optical diffusingelement comprises a microlens array including a collection of a largenumber of independent lenses.
 34. The optical module according to claim33, wherein the light beam scanning device bends the light beam at ascanning origin and irradiates the light beam onto the microlens array,and changes a bending mode of the light beam with time so that anirradiation position of the bent light beam on the microlens arraychanges with time, and each of the independent lenses included in themicrolens array refracts light incident from the scanning origin to forma common irradiation region on the light receiving surface.
 35. Theoptical module according to claim 32, wherein the light beam scanningdevice is a scanning mirror device, a total reflection prism, arefracting prism, or an electro-optic crystal.